diff --git a/docs/STATUS.md b/docs/STATUS.md
index ea1a8f4..28ab970 100644
--- a/docs/STATUS.md
+++ b/docs/STATUS.md
@@ -179,7 +179,7 @@ never by hand.
 | Command                        | Result                                                                                                                                                                                                                                                                                                                                    |
 | ------------------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
 | `pnpm run typecheck`           | clean (tsc strict over packages, tools, tests)                                                                                                                                                                                                                                                                                            |
-| `pnpm run test`                | 556 tests / 31 files �?all passing (all systems + JPL Horizons 独立 golden + interpret + 吉凶 + 合婚 + reading-lint/空话/重复/越界 + validate-answer v2 结构与措辞门禁（约束引用事实豁免+全可见文本安全扫�?资源上限+有界解析入口，非语义正确性证明） + western-rules/ziwei-rules 语义规则 + 版本迁移/回滚/目标白名�?+ PII 隐私护栏 green) |
+| `pnpm run test`                | 675 tests / 33 files �?all passing (all systems + JPL Horizons 独立 golden + interpret + 吉凶 + 合婚 + reading-lint/空话/重复/越界 + validate-answer v2 结构与措辞门禁（约束引用事实豁免+全可见文本安全扫�?资源上限+有界解析入口，非语义正确性证明） + western-rules/ziwei-rules 语义规则 + 版本迁移/回滚/目标白名�?+ PII 隐私护栏 green) |
 | `pnpm run build`               | `engine.mjs` �?2.8 MB + `sbom.cdx.json` + `sbom.spdx.json` (6 runtime deps)                                                                                                                                                                                                                                                               |
 | `pnpm run validate:skill`      | 40 / 40 (incl. scripts/ no-stray-files guard + CycloneDX/SPDX SBOM checks + validate-answer/lint-reading gate-workflow doc checks)                                                                                                                                                                                                        |
 | `pnpm run validate:reading`    | 53 / 53 (topic example libraries + output-spec structure + 无术语区 firewall; offline, no LLM)                                                                                                                                                                                                                                            |
@@ -216,9 +216,10 @@ runnable from a clean copy outside the repo, offline, deterministic.
 ## Open risks
 
 - Western angles/houses are derived in-house (not astronomy-engine); they are validated against
-  the MC=RAMC and eastern-horizon oracles, but an independent golden house-table (e.g. a Swiss
-  Ephemeris reference chart) would further harden them. (Planetary longitudes now HAVE an
-  independent JPL Horizons golden; only the house layer still lacks one.)
+  the MC=RAMC and eastern-horizon oracles and an independent Swiss Ephemeris house golden
+  (swetest 2.10.03, 5 synthetic cases x 5 systems, 12 cusps + angles each, worst measured
+  deviation 0.69 arc-minutes; see packages/western/goldens/README.md). The golden covers
+  normal latitudes; circumpolar instants are contract-tested (HOUSE_SYSTEM_UNAVAILABLE).
 - LMT-era (early 1901+) offsets are whole-minute precision (moment-timezone limitation).
 - Equation of time is an approximation (~tenths of a minute); fine for display, not high-precision.
 - TypeScript pinned to 5.9 while registry `latest` is 7.0; revisit after TS 7 soaks.
diff --git a/docs/VALIDATION.md b/docs/VALIDATION.md
index dd62121..8ad1f31 100644
--- a/docs/VALIDATION.md
+++ b/docs/VALIDATION.md
@@ -59,7 +59,7 @@ the identical table in [STATUS.md](./STATUS.md) ("Commands & results"). Do not h
 resolve a disagreement; re-run the suite and copy the actual count. `pnpm run check:doc-counts`
 re-runs the suite and fails if either doc's `N tests / M files` count drifts from the real run.
 
-- Typecheck: clean. Tests: **556 tests / 31 files �?all passing**. The Western provider
+- Typecheck: clean. Tests: **675 tests / 33 files �?all passing**. The Western provider
   (astronomy-engine, VSOP87 + NOVAS) passes the ADR-0003 �?�?gate two ways: wrapper-consistency
   (vs astronomy-engine's own output) plus an **independent JPL Horizons golden** (10 bodies × 3
   technical epochs fetched from the NASA/JPL Horizons service, query recorded in
@@ -133,11 +133,11 @@ canonical-JSON order independence; deterministic hashing; calculate determinism.
   why it is trustworthy.
 - Western: at least one set cross-checked against JPL/Swiss; main-body positions within �?
   arc-minute; discrete classifications (sign/house changes) must match exactly. (Planetary
-  longitudes: met via the JPL Horizons golden; an independent house table is still open.)
+  longitudes: met via the JPL Horizons golden; house cusps: met via the Swiss Ephemeris house golden.)
 - BaZi/Zi Wei: sourced references, NOT another wrapper of the same core library.
 - Snapshots guard against regressions only; they never become ground truth.
-- Minimum targets: time/location 30 (met: 36), Western 20 (met: 30 �?JPL Horizons golden
-  longitudes), BaZi 40, Zi Wei 20.
+- Minimum targets: time/location 30 (met: 36), Western 20 (met: 55 �?JPL Horizons golden
+  longitudes + 25 Swiss Ephemeris house-cusp sets), BaZi 40, Zi Wei 20.
 
 ## Must-test boundaries (tracked to Phase 2)
 
diff --git a/packages/western/goldens/README.md b/packages/western/goldens/README.md
index 827bc08..4ac9a94 100644
--- a/packages/western/goldens/README.md
+++ b/packages/western/goldens/README.md
@@ -1,4 +1,4 @@
-# Western independent golden fixtures (JPL Horizons)
+# Western independent golden fixtures (JPL Horizons + Swiss Ephemeris)
 
 This directory holds the **independent** ephemeris cross-check of the Western provider
 against authoritative [JPL Horizons](https://ssd.jpl.nasa.gov/horizons/) geocentric
@@ -21,9 +21,91 @@ that layer, plus the Sun cardinal-point anchors).
 Do **not** fabricate values here. When adding rows or epochs, copy them from a real,
 reproducible JPL Horizons query and record the exact query in the fixture's `source` block.
 
+## Swiss Ephemeris house golden — POPULATED
+
+`swiss-ephemeris-houses.json` is the independent house-cusp golden (placidus / koch /
+porphyry / equal / whole-sign) referenced against the Swiss Ephemeris `swetest`
+command-line tool. **Populated** (swetest `Version: 2.10.03`, captured 2026-07-28,
+input time scale UTC via `-utc`): 5 synthetic technical epochs × 5 systems × 12 cusps
+plus ASC/MC/ARMC, transcribed deterministically from a reviewed local capture whose
+per-file SHA-256 (stdout, stderr and argv of all 25 calls + version banner) is recorded
+in the fixture's `source.rawSha256`. Measured worst deviation at population time:
+placidus 0.286′, koch 0.688′, porphyry/equal/whole-sign 0.187′ — per-system
+`toleranceArcmin` is the measured maximum plus headroom (0.5′ / 0.9′ / 0.35′), all under
+the ≤1′ gate (rationale recorded in `toleranceRationale`; the residual is dominated by
+mean-vs-true obliquity). `western-house-golden.test.ts` keeps its fail-closed capture
+gate: a de-populated or half-filled fixture turns the suite red again.
+
+Do **not** edit golden values by hand; regenerate via `tools/generate-house-golden.ts`
+and re-review.
+
+### Source & licensing boundary
+
+- `swetest` is used **only** as a one-off external reference generator. Its numeric output
+  (factual astronomical data for given inputs) is recorded here; the swetest program,
+  sources, binaries and ephemeris data files never enter this repository, the lockfile,
+  the SBOM, the release bundle or CI. Tests run fully offline from the tracked fixture.
+- The reference commands use `-emos` (Moshier). This round's reference commands do not
+  require bringing external ephemeris data files into the repository; no additional
+  precision claim is made here — measured tolerances are recorded in the fixture only
+  after a real capture.
+
+### Capture workflow (two-phase)
+
+1. On a machine with a local `swetest` install, run:
+
+   PowerShell:
+
+   ```
+   $env:SWETEST_PATH = 'C:\path\to\swetest.exe'; node --experimental-strip-types tools/generate-house-golden.ts
+   ```
+
+   POSIX:
+
+   ```
+   SWETEST_PATH=/path/to/swetest node --experimental-strip-types tools/generate-house-golden.ts
+   ```
+
+   The script refuses to run without `SWETEST_PATH` (it never downloads anything) and
+   invokes `swetest -b<DD.MM.YYYY> -utc<HH:MM:SS> -house<lonE>,<lat>,<LETTER> -emos -head`
+   once per sample × system (letters: P=placidus, K=koch, O=porphyry, E=equal(Asc),
+   W=whole-sign), for 5 synthetic technical epochs (see the sample matrix in the script;
+   none of them is real birth data).
+
+2. All output is first written to an untracked staging directory
+   (`.tmp/house-golden-raw.staging-<utc>/`) and atomically renamed to
+   `.tmp/house-golden-raw/` only after every invocation succeeds and parses; a
+   pre-existing capture directory is renamed aside (never deleted, never merged), so
+   stale raw files cannot mix into a fresh capture. Contents:
+   `case-<id>-<system>.stdout.txt` / `.stderr.txt` per invocation,
+   `version.stdout.txt` / `version.stderr.txt`, `manifest.json` (full argv per call,
+   swetest version line, UTC capture time, separate SHA-256 for every stdout/stderr/argv,
+   sample matrix) and `draft-fixture.json` (parsed draft). The script exits non-zero —
+   producing no final directory — on any spawn error, signal, non-zero exit,
+   error-looking stderr, parse failure, missing field, or a quadrant-system output
+   mentioning "Porphyry" on either stream (swetest's silent high-latitude fallback,
+   which this project **rejects**).
+3. The capture is then reviewed (manifest ↔ raw SHA-256 cross-check, draft ↔ raw
+   cross-check, order-of-magnitude sanity against engine output) before being transcribed
+   into the tracked fixture with `status: "populated"`, real `source.version` /
+   `captureDateUtc` / `rawSha256`, and per-system `toleranceArcmin` set to the smallest
+   justified value ≤ 1 arc-minute (rationale recorded in `toleranceRationale`).
+
+### High-latitude boundary
+
+The high-latitude tests in `western-house-golden.test.ts` are fixture-independent engine
+self-assertions. The contract for the quadrant systems (Placidus, Koch) is: whenever the
+geometry is undefined they must throw `HOUSE_SYSTEM_UNAVAILABLE` — never silently fall
+back (swetest falls back to Porphyry there; this project rejects that fallback). Koch's
+guard is the MC degree's own semi-arc (undefined when the MC degree is circumpolar,
+|tan φ · tan δ_MC| > 1); the suite asserts it on synthetic instants VERIFIED against the
+implementation to hit that condition. Whether koch is defined at a given high-latitude
+instant depends on λ_MC at that moment — no blanket "always fails" claim is made.
+
 ## Not covered (still open)
 
-- An independent golden **house table** (e.g. a Swiss Ephemeris reference chart) for the
-  in-house angles/houses — tracked in `docs/STATUS.md` Open risks.
+- The house golden covers normal latitudes only (five synthetic cases between 33.9°S and
+  59.9°N); circumpolar instants are covered by contract tests (throw, no fallback), not
+  by golden values.
 - The sidereal zodiac, true node and asteroids remain `precision: approximate` with their
   own continuity regression; they are intentionally outside this ≤1′ golden.
diff --git a/packages/western/goldens/swiss-ephemeris-houses.json b/packages/western/goldens/swiss-ephemeris-houses.json
new file mode 100644
index 0000000..bd09a1a
--- /dev/null
+++ b/packages/western/goldens/swiss-ephemeris-houses.json
@@ -0,0 +1,362 @@
+{
+  "status": "populated",
+  "note": "Independent Swiss Ephemeris house golden. Populated from a locally reviewed swetest capture (see source block; raw files live in the untracked .tmp/house-golden-raw/ and are identified by SHA-256 below). All sample instants/coordinates are SYNTHETIC technical epochs, not real birth data. Do NOT edit values by hand; regenerate via tools/generate-house-golden.ts and re-review.",
+  "source": {
+    "tool": "swetest (Swiss Ephemeris command-line)",
+    "version": "Version: 2.10.03",
+    "captureDateUtc": "2026-07-28T10:10:32.404Z",
+    "commandTemplate": "SWETEST_PATH=<local path> node --experimental-strip-types tools/generate-house-golden.ts  (per call: swetest -b<DD.MM.YYYY> -utc<HH:MM:SS> -house<lonE>,<lat>,<LETTER> -emos -head)",
+    "referenceInputTimeScale": "UTC",
+    "houseLetterMap": {
+      "placidus": "P",
+      "koch": "K",
+      "porphyry": "O",
+      "equal": "E",
+      "whole-sign": "W"
+    },
+    "coordinateSemantics": "tropical ecliptic of date, geocentric; input longitude east-positive; -emos Moshier (reference command requires no ephemeris data files in the repository)",
+    "docs": [
+      "https://www.astro.com/swisseph-download/doc/swisseph.pdf",
+      "https://www.astro.com/cgi/prep.cgi/swisseph/ae/hcs_P_e.pdf"
+    ],
+    "rawSha256": {
+      "version.stdout.txt": "c6e2c69a85d3e300a14cf7d172450acd201bdb85d7f98d7eabb949dcb94f2ec6",
+      "version.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s1-placidus.stdout.txt": "ac477e7b6d7c334a40afcb5ae3c830e316cfd6e7e1f73a704fbe0950029d2628",
+      "case-s1-placidus.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s1-koch.stdout.txt": "0e9095d2edae135d840d316bb70c22aef80f48f959ed1c84968902ab0a598bc1",
+      "case-s1-koch.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s1-porphyry.stdout.txt": "ae04d038d4f156088c422c3d23fd9652d544fa202beb4d04c34c4769785e1d50",
+      "case-s1-porphyry.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s1-equal.stdout.txt": "da710fca8d93b4ac5d792a7028c6c07bad7af6a295be905013b8976f654314e5",
+      "case-s1-equal.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s1-whole-sign.stdout.txt": "7d56360aa81cb86efea93339974d5d5d5a165f4a33c29f4eccbc4ee4b7eafbd5",
+      "case-s1-whole-sign.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s2-placidus.stdout.txt": "0a3977c275774c81a4b43aceb82ee425d1e8255a0877a712dc644727df5653f8",
+      "case-s2-placidus.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s2-koch.stdout.txt": "9161261f0dd4ed5b06e85d4980fcc5164be21f34dc362703abf64af68df0d91a",
+      "case-s2-koch.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s2-porphyry.stdout.txt": "d90854cc59cf3d5bfaefbab362a9916424209f0517d7cb94e7732bafeb3f0754",
+      "case-s2-porphyry.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s2-equal.stdout.txt": "45cf879dbf453c0f1d671668c0fd5d9b379682734bb761a2274ee87a115ae13f",
+      "case-s2-equal.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s2-whole-sign.stdout.txt": "9c0419d1de429e13e0d7ec5cc169e38fd5223e4e3ad3cf547fea44d55adc8d2e",
+      "case-s2-whole-sign.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s3-placidus.stdout.txt": "5d7b0ae6e79fd3aa6c6e3a3ff7bf1bede8577847366ff9522462c48d34a2e26b",
+      "case-s3-placidus.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s3-koch.stdout.txt": "6985310c22a730ab1bf496cf739e97f8a5ad757a79b61d5c8b5d2dfb6ee2333e",
+      "case-s3-koch.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s3-porphyry.stdout.txt": "c943dfb33d4173c1a1ef14e589e6d276f326c9b42aa4e5114c1604cdac3720a9",
+      "case-s3-porphyry.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s3-equal.stdout.txt": "ce481e783c19722e0b8cdaf5c855d2a91adde78835a2f402132571840faff410",
+      "case-s3-equal.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s3-whole-sign.stdout.txt": "d3c624476ed8dff558ac03892cfdc01c423f14ca0203ee1e7a537b57b09bc66c",
+      "case-s3-whole-sign.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s4-placidus.stdout.txt": "95d5836279f25dec67fd5ea186c60442a28c671eb71aba21688ce1bd82576880",
+      "case-s4-placidus.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s4-koch.stdout.txt": "929084640272484942c041b7b375d361c1d74ddcd5eb9619972812a9ef23e230",
+      "case-s4-koch.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s4-porphyry.stdout.txt": "fbc7fa78929fdbf635a87bd23a00c089519261566e31177988f36dc555f45aec",
+      "case-s4-porphyry.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s4-equal.stdout.txt": "94299d051cc4c4911340bd7834a06976d409d4f8ca270a824be5c600fd29fabe",
+      "case-s4-equal.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s4-whole-sign.stdout.txt": "ec2be8d7ac5d0220f8d356a76064b97ce19e7d0a5e7789fa2dad3334ff982f46",
+      "case-s4-whole-sign.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s5-placidus.stdout.txt": "a84f5674198ddee8ca5df8db08477c32afb66cc05bcfd45c5962d26005f4c373",
+      "case-s5-placidus.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s5-koch.stdout.txt": "86cecc03362300897c2bc45c1901a58e33e378afcba6b2b2e6cb4f1a4912609c",
+      "case-s5-koch.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s5-porphyry.stdout.txt": "d395a9c79d728ba9c21b0d81cb4af49cd96b5064e461a2e54f80fc6b748e6632",
+      "case-s5-porphyry.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s5-equal.stdout.txt": "6c53c3a9019bbefebf1754e4e17064a3eaa3c697c7b982a5ac61dec70d6731a2",
+      "case-s5-equal.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
+      "case-s5-whole-sign.stdout.txt": "06fc8be1d0bfc1421d633afd6b2458d7ef6dbdd4a153bac6fabb819a5fbc18cb",
+      "case-s5-whole-sign.stderr.txt": "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855"
+    }
+  },
+  "toleranceArcmin": {
+    "placidus": 0.5,
+    "koch": 0.9,
+    "porphyry": 0.35,
+    "equal": 0.35,
+    "whole-sign": 0.35
+  },
+  "toleranceRationale": "Measured max wrapped deviation across all 5 cases x (12 cusps + ASC/MC/IC/DESC) at population time, adopted tolerance, and exact margin (tolerance - measured max) per system: placidus 0.285887' -> 0.50' (margin 0.214113'); koch 0.687815' -> 0.90' (margin 0.212185'); porphyry 0.187365' -> 0.35' (margin 0.162635'); equal 0.187365' -> 0.35' (margin 0.162635'); whole-sign 0.187365' -> 0.35' (margin 0.162635'). Tolerance values lie on a 0.05' grid; the margins are exact differences and are NOT themselves rounded. All tolerances stay under the 1' spec ceiling. The residual comes mainly from this engine using the MEAN obliquity (astronomy-engine e_tilt().mobl) while the Swiss reference uses the true obliquity; koch's residual is larger because its cusps are ascendants at shifted sidereal times, which amplifies the obliquity difference at higher latitude (worst case s5, 59.9N).",
+  "cases": [
+    {
+      "id": "s1",
+      "description": "Northern mid-latitude, east longitude (synthetic)",
+      "utcIso": "1990-03-10T00:15:00Z",
+      "latDeg": 30.5,
+      "lonEastDeg": 114.3,
+      "systems": {
+        "placidus": {
+          "cusps": [
+            22.31782822222222, 55.68810133333333, 81.11792216666666, 104.24916869444445,
+            129.37590605555556, 161.07921425, 202.31782822222223, 235.68810133333335,
+            261.1179221666667, 284.24916869444445, 309.37590605555556, 341.07921425
+          ],
+          "ascendant": 22.31782822222222,
+          "mc": 284.24916869444445,
+          "armc": 285.47205291666666
+        },
+        "koch": {
+          "cusps": [
+            22.31782822222222, 54.75415352777778, 81.33188575, 104.24916869444445,
+            132.00789947222222, 165.77248597222223, 202.31782822222223, 234.7541535277778,
+            261.33188574999997, 284.24916869444445, 312.0078994722222, 345.7724859722222
+          ],
+          "ascendant": 22.31782822222222,
+          "mc": 284.24916869444445,
+          "armc": 285.47205291666666
+        },
+        "porphyry": {
+          "cusps": [
+            22.31782822222222, 49.628275055555555, 76.93872188888889, 104.24916869444445,
+            136.9387218888889, 169.62827505555558, 202.31782822222223, 229.62827505555558,
+            256.9387218888889, 284.24916869444445, 316.9387218888889, 349.62827505555555
+          ],
+          "ascendant": 22.31782822222222,
+          "mc": 284.24916869444445,
+          "armc": 285.47205291666666
+        },
+        "equal": {
+          "cusps": [
+            22.31782822222222, 52.317828222222225, 82.31782822222222, 112.31782822222222,
+            142.31782822222223, 172.31782822222223, 202.31782822222223, 232.31782822222223,
+            262.3178282222222, 292.3178282222222, 322.3178282222222, 352.3178282222222
+          ],
+          "ascendant": 22.31782822222222,
+          "mc": 284.24916869444445,
+          "armc": 285.47205291666666
+        },
+        "whole-sign": {
+          "cusps": [0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330],
+          "ascendant": 22.31782822222222,
+          "mc": 284.24916869444445,
+          "armc": 285.47205291666666
+        }
+      }
+    },
+    {
+      "id": "s2",
+      "description": "Northern mid-latitude, west longitude (synthetic)",
+      "utcIso": "2000-07-04T16:00:00Z",
+      "latDeg": 40.7,
+      "lonEastDeg": -74,
+      "systems": {
+        "placidus": {
+          "cusps": [
+            179.17972466666666, 205.15575705555557, 235.51365169444443, 269.0519991388889,
+            302.6237772777778, 333.0682624722222, 359.1797246666667, 25.155757055555554,
+            55.51365169444444, 89.05199913888889, 122.62377727777778, 153.06826247222222
+          ],
+          "ascendant": 179.17972466666666,
+          "mc": 89.05199913888889,
+          "armc": 88.96676416666666
+        },
+        "koch": {
+          "cusps": [
+            179.17972466666666, 208.66641625, 237.89458152777777, 269.0519991388889,
+            300.4680452222222, 329.71232008333334, 359.1797246666667, 28.666416249999997,
+            57.894581527777774, 89.05199913888889, 120.46804522222223, 149.7123200833333
+          ],
+          "ascendant": 179.17972466666666,
+          "mc": 89.05199913888889,
+          "armc": 88.96676416666666
+        },
+        "porphyry": {
+          "cusps": [
+            179.17972466666666, 209.1371494722222, 239.09457430555557, 269.0519991388889,
+            299.0945743055555, 329.13714947222223, 359.1797246666667, 29.137149472222223,
+            59.09457430555556, 89.05199913888889, 119.09457430555555, 149.1371494722222
+          ],
+          "ascendant": 179.17972466666666,
+          "mc": 89.05199913888889,
+          "armc": 88.96676416666666
+        },
+        "equal": {
+          "cusps": [
+            179.17972466666666, 209.17972466666666, 239.17972466666666, 269.1797246666667,
+            299.1797246666667, 329.1797246666667, 359.1797246666667, 29.17972466666667,
+            59.179724666666665, 89.17972466666667, 119.17972466666667, 149.17972466666666
+          ],
+          "ascendant": 179.17972466666666,
+          "mc": 89.05199913888889,
+          "armc": 88.96676416666666
+        },
+        "whole-sign": {
+          "cusps": [150, 180, 210, 240, 270, 300, 330, 0, 30, 60, 90, 120],
+          "ascendant": 179.17972466666666,
+          "mc": 89.05199913888889,
+          "armc": 88.96676416666666
+        }
+      }
+    },
+    {
+      "id": "s3",
+      "description": "Southern mid-latitude, east longitude, December solstice (synthetic)",
+      "utcIso": "2010-12-21T03:30:00Z",
+      "latDeg": -33.9,
+      "lonEastDeg": 151.2,
+      "systems": {
+        "placidus": {
+          "cusps": [
+            19.617875472222224, 47.795211055555555, 78.77088069444444, 111.56475544444444,
+            144.08685108333333, 173.89121566666665, 199.61787547222224, 227.79521105555554,
+            258.77088069444443, 291.5647554444445, 324.08685108333333, 353.89121566666665
+          ],
+          "ascendant": 19.617875472222224,
+          "mc": 291.5647554444445,
+          "armc": 293.3043200833333
+        },
+        "koch": {
+          "cusps": [
+            19.617875472222224, 48.77214158333333, 78.17887161111112, 111.56475544444444,
+            140.64917383333332, 169.989634, 199.61787547222224, 228.77214158333334,
+            258.1788716111111, 291.5647554444445, 320.64917383333335, 349.989634
+          ],
+          "ascendant": 19.617875472222224,
+          "mc": 291.5647554444445,
+          "armc": 293.3043200833333
+        },
+        "porphyry": {
+          "cusps": [
+            19.617875472222224, 50.26683547222222, 80.91579544444446, 111.56475544444444,
+            140.91579544444446, 170.26683547222223, 199.61787547222224, 230.26683547222223,
+            260.9157954444444, 291.5647554444445, 320.9157954444444, 350.2668354722222
+          ],
+          "ascendant": 19.617875472222224,
+          "mc": 291.5647554444445,
+          "armc": 293.3043200833333
+        },
+        "equal": {
+          "cusps": [
+            19.617875472222224, 49.617875472222224, 79.61787547222221, 109.61787547222221,
+            139.61787547222224, 169.61787547222224, 199.61787547222224, 229.61787547222224,
+            259.61787547222224, 289.61787547222224, 319.61787547222224, 349.61787547222224
+          ],
+          "ascendant": 19.617875472222224,
+          "mc": 291.5647554444445,
+          "armc": 293.3043200833333
+        },
+        "whole-sign": {
+          "cusps": [0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330],
+          "ascendant": 19.617875472222224,
+          "mc": 291.5647554444445,
+          "armc": 293.3043200833333
+        }
+      }
+    },
+    {
+      "id": "s4",
+      "description": "Near-equator low latitude, earlier era (synthetic)",
+      "utcIso": "1975-01-30T12:00:00Z",
+      "latDeg": 1.35,
+      "lonEastDeg": 103.8,
+      "systems": {
+        "placidus": {
+          "cusps": [
+            140.86329644444444, 172.32664066666666, 204.64760541666666, 235.2494834722222,
+            263.6638773333333, 291.52627530555554, 320.8632964444445, 352.32664066666666,
+            24.647605416666668, 55.249483472222224, 83.66387733333335, 111.52627530555556
+          ],
+          "ascendant": 140.86329644444444,
+          "mc": 55.249483472222224,
+          "armc": 52.90541897222222
+        },
+        "koch": {
+          "cusps": [
+            140.86329644444444, 172.5199063888889, 204.81547502777778, 235.2494834722222,
+            263.7339943055556, 291.54841052777783, 320.8632964444445, 352.5199063888889,
+            24.81547502777778, 55.249483472222224, 83.73399430555556, 111.54841052777778
+          ],
+          "ascendant": 140.86329644444444,
+          "mc": 55.249483472222224,
+          "armc": 52.90541897222222
+        },
+        "porphyry": {
+          "cusps": [
+            140.86329644444444, 172.32535877777778, 203.78742113888887, 235.2494834722222,
+            263.78742113888893, 292.32535877777775, 320.8632964444445, 352.32535877777775,
+            23.78742113888889, 55.249483472222224, 83.78742113888889, 112.32535877777778
+          ],
+          "ascendant": 140.86329644444444,
+          "mc": 55.249483472222224,
+          "armc": 52.90541897222222
+        },
+        "equal": {
+          "cusps": [
+            140.86329644444444, 170.86329644444444, 200.86329644444444, 230.86329644444444,
+            260.8632964444445, 290.8632964444445, 320.8632964444445, 350.8632964444445,
+            20.863296444444448, 50.863296444444444, 80.86329644444444, 110.86329644444444
+          ],
+          "ascendant": 140.86329644444444,
+          "mc": 55.249483472222224,
+          "armc": 52.90541897222222
+        },
+        "whole-sign": {
+          "cusps": [120, 150, 180, 210, 240, 270, 300, 330, 0, 30, 60, 90],
+          "ascendant": 140.86329644444444,
+          "mc": 55.249483472222224,
+          "armc": 52.90541897222222
+        }
+      }
+    },
+    {
+      "id": "s5",
+      "description": "Higher (but well-defined) northern latitude, summer (synthetic)",
+      "utcIso": "2024-06-15T18:45:00Z",
+      "latDeg": 59.9,
+      "lonEastDeg": 10.75,
+      "systems": {
+        "placidus": {
+          "cusps": [
+            246.09074258333334, 284.6197638055556, 340.61999636111113, 17.935423305555556,
+            39.91684583333333, 54.69598072222222, 66.09074258333332, 104.61976380555555,
+            160.6199963611111, 197.93542330555556, 219.91684583333333, 234.69598072222223
+          ],
+          "ascendant": 246.09074258333334,
+          "mc": 197.93542330555556,
+          "armc": 196.5396851388889
+        },
+        "koch": {
+          "cusps": [
+            246.09074258333334, 264.81100141666667, 294.2910993055556, 17.935423305555556,
+            33.881787833333334, 49.744796666666666, 66.09074258333332, 84.81100141666667,
+            114.29109930555555, 197.93542330555556, 213.88178783333333, 229.74479666666664
+          ],
+          "ascendant": 246.09074258333334,
+          "mc": 197.93542330555556,
+          "armc": 196.5396851388889
+        },
+        "porphyry": {
+          "cusps": [
+            246.09074258333334, 290.0389695, 333.9871963888889, 17.935423305555556,
+            33.98719638888889, 50.0389695, 66.09074258333332, 110.0389695, 153.98719638888886,
+            197.93542330555556, 213.98719638888886, 230.0389695
+          ],
+          "ascendant": 246.09074258333334,
+          "mc": 197.93542330555556,
+          "armc": 196.5396851388889
+        },
+        "equal": {
+          "cusps": [
+            246.09074258333334, 276.09074258333334, 306.09074258333334, 336.09074258333334,
+            6.090742583333333, 36.09074258333334, 66.09074258333332, 96.09074258333332,
+            126.09074258333332, 156.09074258333334, 186.09074258333334, 216.09074258333334
+          ],
+          "ascendant": 246.09074258333334,
+          "mc": 197.93542330555556,
+          "armc": 196.5396851388889
+        },
+        "whole-sign": {
+          "cusps": [240, 270, 300, 330, 0, 30, 60, 90, 120, 150, 180, 210],
+          "ascendant": 246.09074258333334,
+          "mc": 197.93542330555556,
+          "armc": 196.5396851388889
+        }
+      }
+    }
+  ]
+}
diff --git a/packages/western/src/houses.ts b/packages/western/src/houses.ts
index 633facf..17cbf28 100644
--- a/packages/western/src/houses.ts
+++ b/packages/western/src/houses.ts
@@ -120,15 +120,36 @@ export function computeHouseCusps(
       break;
     }
     case 'koch': {
-      // Birthplace houses: trisect the ASCENDANT's own semi-arc (constant), so the
-      // cusp right ascensions are linear in RAMC — no iteration needed.
-      const declAsc = declinationOf(ascendant, eps);
-      const sda = semiDiurnalArc(declAsc, latDeg);
-      const sna = 180 - sda;
-      cusps[10] = raToLambda(ramc + sda / 3, eps); // house 11
-      cusps[11] = raToLambda(ramc + (2 * sda) / 3, eps); // house 12
-      cusps[1] = raToLambda(ramc + sda + sna / 3, eps); // house 2
-      cusps[2] = raToLambda(ramc + sda + (2 * sna) / 3, eps); // house 3
+      // Koch (GOH / "Birthplace") houses — independent derivation, no Swiss
+      // Ephemeris code used or consulted (Swiss serves only as an external
+      // numeric acceptance oracle via the tracked golden fixture).
+      //
+      // Definition (Koch & Schäck, "Häusertabellen des Geburtsortes", 1971;
+      // described in swisseph.pdf §house systems and Holden, "The Elements of
+      // House Division"): the MC ecliptic degree needed SDA degrees of
+      // sidereal time (its own semi-diurnal arc) to travel from the eastern
+      // horizon to the meridian. Trisecting that TIME interval, the
+      // intermediate cusps are the ASCENDANTS at the shifted sidereal times:
+      //   cusp 11 = Asc(RAMC − 2·SDA/3)   cusp 12 = Asc(RAMC − SDA/3)
+      //   cusp  2 = Asc(RAMC + SDA/3)     cusp  3 = Asc(RAMC + 2·SDA/3)
+      // with SDA = acos(−tan φ · tan δ_MC) and δ_MC = asin(sin ε · sin λ_MC)
+      // (standard spherical-astronomy formulas). Endpoint self-consistency:
+      // Asc(RAMC − SDA) = λ_MC (the MC degree was rising) and
+      // Asc(RAMC + SDA) = λ_IC (the IC degree rises as the MC degree sets),
+      // so the trisection interpolates exactly between the four angles.
+      //
+      // The system is geometrically undefined when the MC degree is
+      // circumpolar (|tan φ · tan δ_MC| > 1, beyond the polar circles);
+      // semiDiurnalArc then raises HOUSE_SYSTEM_UNAVAILABLE — no silent
+      // fallback. Known limitation: this engine uses the MEAN obliquity
+      // (e_tilt().mobl) while the reference uses the true obliquity, leaving
+      // a sub-arcminute residual of the same order as Placidus (~0.3').
+      const declMc = declinationOf(mc, eps);
+      const sda = semiDiurnalArc(declMc, latDeg);
+      cusps[10] = ascendantLongitude(norm360(ramc - (2 * sda) / 3), latDeg, eps); // house 11
+      cusps[11] = ascendantLongitude(norm360(ramc - sda / 3), latDeg, eps); // house 12
+      cusps[1] = ascendantLongitude(norm360(ramc + sda / 3), latDeg, eps); // house 2
+      cusps[2] = ascendantLongitude(norm360(ramc + (2 * sda) / 3), latDeg, eps); // house 3
       break;
     }
     case 'placidus': {
diff --git a/packages/western/test/houses.test.ts b/packages/western/test/houses.test.ts
index d9cfe37..0e2f02e 100644
--- a/packages/western/test/houses.test.ts
+++ b/packages/western/test/houses.test.ts
@@ -130,15 +130,19 @@ describe('house systems', () => {
   });
 
   it('quadrant systems fail at high latitude instead of fabricating cusps', () => {
-    // At 78°N, some semi-arc becomes undefined (|tan φ·tan δ| > 1), so Placidus/Koch
-    // must raise HOUSE_SYSTEM_UNAVAILABLE rather than emit a made-up cusp.
-    let threw = false;
-    try {
-      computeHouseCusps('placidus', dateMs, 78, lon);
-    } catch (err) {
-      threw = err instanceof EngineError && err.code === ERROR_CODES.HOUSE_SYSTEM_UNAVAILABLE;
+    // At 78°N on this instant, the relevant semi-arc is undefined
+    // (|tan φ·tan δ| > 1): Placidus hits it in its per-cusp iteration and
+    // koch on the MC degree itself (verified: both throw here), so they must
+    // raise HOUSE_SYSTEM_UNAVAILABLE rather than emit a made-up cusp.
+    for (const system of ['placidus', 'koch'] as const) {
+      let threw = false;
+      try {
+        computeHouseCusps(system, dateMs, 78, lon);
+      } catch (err) {
+        threw = err instanceof EngineError && err.code === ERROR_CODES.HOUSE_SYSTEM_UNAVAILABLE;
+      }
+      expect(threw, `${system} must throw HOUSE_SYSTEM_UNAVAILABLE`).toBe(true);
     }
-    expect(threw).toBe(true);
   });
 });
 
diff --git a/packages/western/test/western-house-golden.test.ts b/packages/western/test/western-house-golden.test.ts
new file mode 100644
index 0000000..dd906d2
--- /dev/null
+++ b/packages/western/test/western-house-golden.test.ts
@@ -0,0 +1,234 @@
+// Independent Swiss Ephemeris house golden — all fixture samples are
+// SYNTHETIC technical epochs (not real birth data). This suite is
+// FAIL-CLOSED: while the tracked fixture is still the PENDING_CAPTURE
+// skeleton, the gate test below FAILS (never skips), so the suite cannot
+// silently look green without real captured reference data.
+import { readFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, expect, it } from 'vitest';
+import { ERROR_CODES, EngineError } from '@ming/contracts';
+import { deltaLon, norm360 } from '../src/ephemeris.ts';
+import { computeHouseCusps, houseOfLongitude, type HouseSystemId } from '../src/houses.ts';
+
+const here = dirname(fileURLToPath(import.meta.url));
+const fixturePath = join(here, '..', 'goldens', 'swiss-ephemeris-houses.json');
+
+const SYSTEMS: HouseSystemId[] = ['placidus', 'koch', 'porphyry', 'equal', 'whole-sign'];
+
+interface GoldenSystem {
+  cusps: number[]; // index 0 = house 1 ... index 11 = house 12
+  ascendant: number;
+  mc: number;
+  armc: number | null;
+}
+interface GoldenCase {
+  id: string;
+  description: string;
+  utcIso: string;
+  latDeg: number;
+  lonEastDeg: number;
+  systems: Record<string, GoldenSystem>;
+}
+interface GoldenFixture {
+  status: string;
+  source: {
+    version: string | null;
+    captureDateUtc: string | null;
+    rawSha256: Record<string, string>;
+  };
+  toleranceArcmin: Record<string, number | null>;
+  toleranceRationale: string | null;
+  cases: GoldenCase[];
+}
+
+const fixture: GoldenFixture = JSON.parse(readFileSync(fixturePath, 'utf8'));
+
+/** Wrapped angular distance in ARCMINUTES. */
+function wrappedArcmin(a: number, b: number): number {
+  return Math.abs(deltaLon(a, b)) * 60;
+}
+
+describe('western house golden: fail-closed capture gate', () => {
+  it('fixture is populated with captured Swiss Ephemeris data (fails while PENDING_CAPTURE)', () => {
+    // This test MUST stay red until the fixture is populated from a real,
+    // reviewed swetest capture. Never skip it, never soften it: a pending or
+    // half-filled fixture is NOT a passing state.
+    expect(fixture.status).toBe('populated');
+    expect(fixture.source.version).toBeTruthy();
+    expect(fixture.source.captureDateUtc).toBeTruthy();
+    expect(Object.keys(fixture.source.rawSha256).length).toBeGreaterThan(0);
+    expect(fixture.cases.length).toBeGreaterThanOrEqual(5);
+    for (const c of fixture.cases) {
+      for (const sys of SYSTEMS) {
+        expect(c.systems[sys], `case ${c.id} missing system ${sys}`).toBeDefined();
+        expect(c.systems[sys]!.cusps).toHaveLength(12);
+      }
+    }
+    for (const sys of SYSTEMS) {
+      const tol = fixture.toleranceArcmin[sys];
+      expect(
+        typeof tol === 'number' && tol > 0 && tol <= 1,
+        `toleranceArcmin.${sys} must be a positive number <= 1 arc-minute, got ${tol}`,
+      ).toBe(true);
+    }
+    expect(fixture.toleranceRationale).toBeTruthy();
+  });
+});
+
+// Golden comparisons: only meaningful once populated. Guarded by a plain
+// conditional (NOT it.skip) so the pending state yields zero green golden
+// assertions while the gate test above is red.
+if (fixture.status === 'populated') {
+  describe('western house golden: engine vs Swiss Ephemeris', () => {
+    for (const c of fixture.cases) {
+      const dateMs = Date.parse(c.utcIso);
+      describe(`${c.id} (${c.description})`, () => {
+        for (const sys of SYSTEMS) {
+          const golden = c.systems[sys]!;
+          const tol = fixture.toleranceArcmin[sys] as number;
+
+          it(`${sys}: angles (ASC/MC/IC/DESC) within ${tol}'`, () => {
+            const r = computeHouseCusps(sys, dateMs, c.latDeg, c.lonEastDeg);
+            expect(wrappedArcmin(r.ascendant, golden.ascendant)).toBeLessThanOrEqual(tol);
+            expect(wrappedArcmin(r.mc, golden.mc)).toBeLessThanOrEqual(tol);
+            // IC and Descendant are derived (+180°) — assert against the
+            // golden-derived values so a sign/quadrant error cannot hide.
+            expect(wrappedArcmin(r.ic, norm360(golden.mc + 180))).toBeLessThanOrEqual(tol);
+            expect(
+              wrappedArcmin(r.descendant, norm360(golden.ascendant + 180)),
+            ).toBeLessThanOrEqual(tol);
+          });
+
+          it(`${sys}: all 12 cusps within ${tol}'`, () => {
+            const r = computeHouseCusps(sys, dateMs, c.latDeg, c.lonEastDeg);
+            for (let i = 0; i < 12; i++) {
+              expect(
+                wrappedArcmin(r.cusps[i]!, golden.cusps[i]!),
+                `house ${i + 1}: engine=${r.cusps[i]} golden=${golden.cusps[i]}`,
+              ).toBeLessThanOrEqual(tol);
+            }
+          });
+
+          it(`${sys}: golden cusp ring closes to 360 degrees`, () => {
+            // Ring consistency of the REFERENCE data itself: successive cusp
+            // gaps (forward along the ecliptic) must sum to a full circle.
+            let sum = 0;
+            for (let i = 0; i < 12; i++) {
+              const a = golden.cusps[i]!;
+              const b = golden.cusps[(i + 1) % 12]!;
+              sum += norm360(b - a);
+            }
+            expect(Math.abs(sum - 360)).toBeLessThanOrEqual(1e-6);
+          });
+        }
+
+        it('equal: cusps are exactly ASC + 30k (discrete definition)', () => {
+          const r = computeHouseCusps('equal', dateMs, c.latDeg, c.lonEastDeg);
+          for (let i = 0; i < 12; i++) {
+            expect(wrappedArcmin(r.cusps[i]!, norm360(r.ascendant + 30 * i))).toBeLessThanOrEqual(
+              1e-6,
+            );
+          }
+        });
+
+        it('whole-sign: every cusp is an exact 30-degree sign boundary containing ASC in house 1', () => {
+          const r = computeHouseCusps('whole-sign', dateMs, c.latDeg, c.lonEastDeg);
+          for (let i = 0; i < 12; i++) {
+            expect(r.cusps[i]! % 30).toBeCloseTo(0, 9);
+          }
+          const ascSignStart = Math.floor(r.ascendant / 30) * 30;
+          expect(r.cusps[0]).toBeCloseTo(ascSignStart, 9);
+        });
+
+        it('houseOfLongitude: a point exactly on a cusp belongs to that house (equal + placidus)', () => {
+          for (const sys of ['equal', 'placidus'] as const) {
+            const r = computeHouseCusps(sys, dateMs, c.latDeg, c.lonEastDeg);
+            // Exactly on cusp of house 4 -> must report house 4.
+            expect(houseOfLongitude(r.cusps, r.cusps[3]!)).toBe(4);
+          }
+        });
+      });
+    }
+  });
+}
+
+describe('western house golden: high-latitude boundary (engine self-assertion, fixture-independent)', () => {
+  // Contract for quadrant systems (Placidus, Koch): whenever the geometry is
+  // undefined they must raise HOUSE_SYSTEM_UNAVAILABLE — never silently fall
+  // back (Swiss Ephemeris swetest falls back to Porphyry there; this project
+  // rejects that fallback). Koch's guard is the MC degree's own semi-arc
+  // (undefined when the MC degree is circumpolar); the koch samples below
+  // were VERIFIED against the implementation to hit that condition. This
+  // does not claim koch fails at every high-latitude instant — whether it
+  // does depends on λ_MC at the moment. These assertions deliberately do
+  // NOT depend on the golden fixture.
+  const HIGH_LAT_CASES = [
+    {
+      name: 'north circumpolar (synthetic)',
+      dateMs: Date.UTC(2001, 5, 21, 0, 0),
+      lat: 66.8,
+      lon: 25.7,
+    },
+    {
+      name: 'south deep-polar (synthetic)',
+      dateMs: Date.UTC(2013, 0, 10, 12, 0),
+      lat: -75.0,
+      lon: 0.0,
+    },
+  ];
+
+  for (const { name, dateMs, lat, lon } of HIGH_LAT_CASES) {
+    it(`${name}: placidus throws HOUSE_SYSTEM_UNAVAILABLE (no Porphyry fallback accepted)`, () => {
+      let thrown: unknown;
+      try {
+        computeHouseCusps('placidus', dateMs, lat, lon);
+      } catch (e) {
+        thrown = e;
+      }
+      expect(thrown).toBeInstanceOf(EngineError);
+      expect((thrown as EngineError).code).toBe(ERROR_CODES.HOUSE_SYSTEM_UNAVAILABLE);
+    });
+
+    for (const sys of ['whole-sign', 'equal', 'porphyry'] as const) {
+      it(`${name}: ${sys} still returns a full cusp ring`, () => {
+        const r = computeHouseCusps(sys, dateMs, lat, lon);
+        expect(r.cusps).toHaveLength(12);
+        for (const cusp of r.cusps) {
+          expect(Number.isFinite(cusp)).toBe(true);
+        }
+      });
+    }
+  }
+
+  // Koch circumpolar-MC samples: at these synthetic instants the MC degree's
+  // declination satisfies |tan φ · tan δ_MC| > 1 (verified by probing the
+  // implementation across the day at each site), so koch is geometrically
+  // undefined and must throw — not fall back.
+  const KOCH_CIRCUMPOLAR_CASES = [
+    {
+      name: 'north circumpolar MC (synthetic, 66.8N 2001-06-21T10:00Z)',
+      dateMs: Date.UTC(2001, 5, 21, 10, 0),
+      lat: 66.8,
+      lon: 25.7,
+    },
+    {
+      name: 'south circumpolar MC (synthetic, 75S 2013-01-10T12:00Z)',
+      dateMs: Date.UTC(2013, 0, 10, 12, 0),
+      lat: -75.0,
+      lon: 0.0,
+    },
+  ];
+  for (const { name, dateMs, lat, lon } of KOCH_CIRCUMPOLAR_CASES) {
+    it(`${name}: koch throws HOUSE_SYSTEM_UNAVAILABLE (no Porphyry fallback accepted)`, () => {
+      let thrown: unknown;
+      try {
+        computeHouseCusps('koch', dateMs, lat, lon);
+      } catch (e) {
+        thrown = e;
+      }
+      expect(thrown).toBeInstanceOf(EngineError);
+      expect((thrown as EngineError).code).toBe(ERROR_CODES.HOUSE_SYSTEM_UNAVAILABLE);
+    });
+  }
+});
diff --git a/skills/calculate-birth-charts/scripts/dist/engine.mjs b/skills/calculate-birth-charts/scripts/dist/engine.mjs
index e947014..33afa74 100644
--- a/skills/calculate-birth-charts/scripts/dist/engine.mjs
+++ b/skills/calculate-birth-charts/scripts/dist/engine.mjs
@@ -51519,13 +51519,12 @@ function computeHouseCusps(system, dateMs, latDeg, lonEastDeg) {
       break;
     }
     case "koch": {
-      const declAsc = declinationOf(ascendant, eps);
-      const sda = semiDiurnalArc(declAsc, latDeg);
-      const sna = 180 - sda;
-      cusps[10] = raToLambda(ramc + sda / 3, eps);
-      cusps[11] = raToLambda(ramc + 2 * sda / 3, eps);
-      cusps[1] = raToLambda(ramc + sda + sna / 3, eps);
-      cusps[2] = raToLambda(ramc + sda + 2 * sna / 3, eps);
+      const declMc = declinationOf(mc, eps);
+      const sda = semiDiurnalArc(declMc, latDeg);
+      cusps[10] = ascendantLongitude(norm360(ramc - 2 * sda / 3), latDeg, eps);
+      cusps[11] = ascendantLongitude(norm360(ramc - sda / 3), latDeg, eps);
+      cusps[1] = ascendantLongitude(norm360(ramc + sda / 3), latDeg, eps);
+      cusps[2] = ascendantLongitude(norm360(ramc + 2 * sda / 3), latDeg, eps);
       break;
     }
     case "placidus": {
diff --git a/tools/generate-house-golden.ts b/tools/generate-house-golden.ts
new file mode 100644
index 0000000..115e4be
--- /dev/null
+++ b/tools/generate-house-golden.ts
@@ -0,0 +1,357 @@
+import { spawnSync } from 'node:child_process';
+import { createHash } from 'node:crypto';
+import { existsSync, mkdirSync, renameSync, writeFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { parseSwetestHouses } from './swetest-parse.ts';
+
+/**
+ * ONE-TIME external reference generator for the Western house golden.
+ *
+ * Runs a locally-installed Swiss Ephemeris `swetest` binary (path supplied
+ * EXPLICITLY via the SWETEST_PATH environment variable — this script never
+ * downloads anything, never adds a dependency, and is not part of the verify
+ * chain or the published Skill) and captures raw house-cusp output for the
+ * synthetic sample matrix below.
+ *
+ * Output protocol (everything under the UNTRACKED `.tmp/` tree):
+ *   1. All files are first written to a fresh staging directory
+ *      `.tmp/house-golden-raw.staging-<utc>/`.
+ *   2. Only after ALL invocations succeed, ALL output parses, and both
+ *      manifest.json and draft-fixture.json are written, the staging
+ *      directory is atomically renamed to `.tmp/house-golden-raw/`. An
+ *      existing `.tmp/house-golden-raw/` is first renamed aside to
+ *      `.tmp/house-golden-raw.replaced-<utc>/` — never deleted, and stale
+ *      raw files can never mix into a fresh capture.
+ *   3. On ANY failure the script exits 1, the staging directory stays where
+ *      it is, and the final directory is never created or touched.
+ *
+ * Per-invocation artifacts inside the directory:
+ *   - case-<id>-<system>.stdout.txt / case-<id>-<system>.stderr.txt
+ *   - version.stdout.txt / version.stderr.txt   (banner run)
+ *   - manifest.json   full argv per call, version line, capture UTC instant,
+ *                     separate SHA-256 for each stdout/stderr/argv, matrix
+ *   - draft-fixture.json  parsed draft (cusps 1-12, Asc, MC, ARMC) for HUMAN
+ *                     REVIEW before being copied into the tracked fixture
+ *
+ * The tracked fixture `packages/western/goldens/swiss-ephemeris-houses.json`
+ * is NEVER written by this script — populating it is a deliberate, reviewed
+ * step (see packages/western/goldens/README.md).
+ *
+ * Fail-closed: a spawn error, a signal, a non-zero exit, an error-looking
+ * stderr, a Porphyry-fallback hint for a quadrant system, any parse failure
+ * or any missing field aborts with exit 1. Failure messages are structural
+ * only — raw external output is written to the untracked staging files, not
+ * echoed into logs.
+ *
+ * All sample instants/coordinates are SYNTHETIC technical epochs — not any
+ * real person's birth data. Sample instants are UTC and are passed to swetest
+ * via `-utc` (NOT `-ut`, which means UT1).
+ */
+
+const here = dirname(fileURLToPath(import.meta.url));
+const root = join(here, '..');
+const tmpRoot = join(root, '.tmp');
+const finalDir = join(tmpRoot, 'house-golden-raw');
+
+/** Swiss Ephemeris house-system letters for the five systems this engine implements. */
+const HOUSE_LETTER: Record<string, string> = {
+  placidus: 'P',
+  koch: 'K',
+  porphyry: 'O',
+  equal: 'E',
+  'whole-sign': 'W',
+};
+
+interface SampleCase {
+  id: string;
+  description: string;
+  utc: { y: number; mo: number; d: number; h: number; mi: number; s: number };
+  latDeg: number;
+  lonEastDeg: number;
+}
+
+/** Synthetic technical sample matrix (NOT real birth data). */
+const CASES: SampleCase[] = [
+  {
+    id: 's1',
+    description: 'Northern mid-latitude, east longitude (synthetic)',
+    utc: { y: 1990, mo: 3, d: 10, h: 0, mi: 15, s: 0 },
+    latDeg: 30.5,
+    lonEastDeg: 114.3,
+  },
+  {
+    id: 's2',
+    description: 'Northern mid-latitude, west longitude (synthetic)',
+    utc: { y: 2000, mo: 7, d: 4, h: 16, mi: 0, s: 0 },
+    latDeg: 40.7,
+    lonEastDeg: -74.0,
+  },
+  {
+    id: 's3',
+    description: 'Southern mid-latitude, east longitude, December solstice (synthetic)',
+    utc: { y: 2010, mo: 12, d: 21, h: 3, mi: 30, s: 0 },
+    latDeg: -33.9,
+    lonEastDeg: 151.2,
+  },
+  {
+    id: 's4',
+    description: 'Near-equator low latitude, earlier era (synthetic)',
+    utc: { y: 1975, mo: 1, d: 30, h: 12, mi: 0, s: 0 },
+    latDeg: 1.35,
+    lonEastDeg: 103.8,
+  },
+  {
+    id: 's5',
+    description: 'Higher (but well-defined) northern latitude, summer (synthetic)',
+    utc: { y: 2024, mo: 6, d: 15, h: 18, mi: 45, s: 0 },
+    latDeg: 59.9,
+    lonEastDeg: 10.75,
+  },
+];
+
+function sha256(buf: string | Buffer): string {
+  return createHash('sha256').update(buf).digest('hex');
+}
+
+function pad2(n: number): string {
+  return String(n).padStart(2, '0');
+}
+
+/** swetest date argument: -bDD.MM.YYYY  (gregorian) */
+function dateArg(c: SampleCase): string {
+  return `-b${pad2(c.utc.d)}.${pad2(c.utc.mo)}.${c.utc.y}`;
+}
+/**
+ * swetest UTC argument: -utcHH:MM:SS — input time scale is UTC (matches the
+ * samples' utcIso field), NOT -ut which means UT1.
+ */
+function utcArg(c: SampleCase): string {
+  return `-utc${pad2(c.utc.h)}:${pad2(c.utc.mi)}:${pad2(c.utc.s)}`;
+}
+/** swetest house argument: -house<lonE>,<lat>,<letter>  (east-positive longitude) */
+function houseArg(c: SampleCase, letter: string): string {
+  return `-house${c.lonEastDeg},${c.latDeg},${letter}`;
+}
+
+interface RunResult {
+  stdout: string;
+  stderr: string;
+}
+
+/**
+ * Run swetest once, fail-closed. Any spawn error, signal (incl. timeout) or
+ * non-zero exit aborts immediately — a non-empty stdout is NOT a pass.
+ * Failure messages stay structural; raw output is never echoed into logs.
+ */
+function runSwetestOrExit(swetestPath: string, argv: string[], label: string): RunResult {
+  const res = spawnSync(swetestPath, argv, { encoding: 'utf8', timeout: 60_000 });
+  if (res.error) {
+    process.stdout.write(`[FAIL] swetest could not be spawned for ${label} (spawn error).\n`);
+    process.exit(1);
+  }
+  if (res.signal !== null) {
+    process.stdout.write(
+      `[FAIL] swetest was terminated by a signal for ${label} (possible timeout).\n`,
+    );
+    process.exit(1);
+  }
+  if (res.status !== 0) {
+    process.stdout.write(`[FAIL] swetest exited with status ${res.status} for ${label}.\n`);
+    process.exit(1);
+  }
+  return { stdout: res.stdout ?? '', stderr: res.stderr ?? '' };
+}
+
+function main(): void {
+  const swetestPath = process.env.SWETEST_PATH;
+  if (!swetestPath) {
+    process.stdout.write(
+      '[FAIL] SWETEST_PATH is not set.\n' +
+        '\n' +
+        'This one-time generator requires a locally installed Swiss Ephemeris\n' +
+        '`swetest` binary supplied EXPLICITLY via the environment:\n' +
+        '\n' +
+        '  PowerShell:\n' +
+        "    $env:SWETEST_PATH = 'C:\\path\\to\\swetest.exe'; node --experimental-strip-types tools/generate-house-golden.ts\n" +
+        '  POSIX:\n' +
+        '    SWETEST_PATH=/path/to/swetest node --experimental-strip-types tools/generate-house-golden.ts\n' +
+        '\n' +
+        'The script never downloads anything and adds no dependency. See\n' +
+        'packages/western/goldens/README.md for the full capture workflow.\n',
+    );
+    process.exit(1);
+  }
+
+  const stamp = new Date().toISOString().replace(/[:.]/g, '-');
+  const stagingDir = join(tmpRoot, `house-golden-raw.staging-${stamp}`);
+  mkdirSync(stagingDir, { recursive: true });
+
+  // Capture the tool banner for provenance (swetest -h prints version+usage).
+  const versionArgv = ['-h'];
+  const versionRun = runSwetestOrExit(swetestPath, versionArgv, 'version banner');
+  writeFileSync(join(stagingDir, 'version.stdout.txt'), versionRun.stdout, 'utf8');
+  writeFileSync(join(stagingDir, 'version.stderr.txt'), versionRun.stderr, 'utf8');
+  // Only an explicit `Version:` line is an auditable tool identifier — never
+  // fall back to descriptive lines that merely mention swetest.
+  const versionLine =
+    `${versionRun.stdout}\n${versionRun.stderr}`
+      .split(/\r?\n/)
+      .map((l) => l.trim())
+      .find((l) => /^Version:\s*\S/.test(l)) ?? null;
+  if (!versionLine) {
+    process.stdout.write('[FAIL] could not find a `Version:` line in the swetest help output.\n');
+    process.exit(1);
+  }
+
+  const manifest: {
+    generatedAtUtc: string;
+    swetestPathNote: string;
+    versionLine: string;
+    version: {
+      argv: string[];
+      argvSha256: string;
+      stdoutFile: string;
+      stdoutSha256: string;
+      stderrFile: string;
+      stderrSha256: string;
+    };
+    calls: {
+      caseId: string;
+      system: string;
+      argv: string[];
+      argvSha256: string;
+      stdoutFile: string;
+      stdoutSha256: string;
+      stderrFile: string;
+      stderrSha256: string;
+    }[];
+    cases: SampleCase[];
+    referenceInputTimeScale: string;
+    coordinateSemantics: string;
+  } = {
+    generatedAtUtc: new Date().toISOString(),
+    swetestPathNote:
+      'local path supplied via SWETEST_PATH env; binary is NOT part of this repository',
+    versionLine,
+    version: {
+      argv: versionArgv,
+      argvSha256: sha256(JSON.stringify(versionArgv)),
+      stdoutFile: 'version.stdout.txt',
+      stdoutSha256: sha256(versionRun.stdout),
+      stderrFile: 'version.stderr.txt',
+      stderrSha256: sha256(versionRun.stderr),
+    },
+    calls: [],
+    cases: CASES,
+    referenceInputTimeScale: 'UTC',
+    coordinateSemantics:
+      'tropical ecliptic of date, geocentric; input longitude east-positive; -emos Moshier (reference command requires no ephemeris data files in the repository)',
+  };
+
+  const draft: {
+    note: string;
+    cases: {
+      id: string;
+      description: string;
+      utcIso: string;
+      latDeg: number;
+      lonEastDeg: number;
+      systems: Record<
+        string,
+        { cusps: number[]; ascendant: number; mc: number; armc: number | null }
+      >;
+    }[];
+  } = {
+    note: 'DRAFT parsed from raw swetest output — requires human review before entering the tracked fixture. All samples are synthetic technical epochs.',
+    cases: [],
+  };
+
+  for (const c of CASES) {
+    const utcIso = `${c.utc.y}-${pad2(c.utc.mo)}-${pad2(c.utc.d)}T${pad2(c.utc.h)}:${pad2(c.utc.mi)}:${pad2(c.utc.s)}Z`;
+    const systems: Record<
+      string,
+      { cusps: number[]; ascendant: number; mc: number; armc: number | null }
+    > = {};
+    for (const [system, letter] of Object.entries(HOUSE_LETTER)) {
+      const label = `${c.id}/${system}`;
+      const argv = [dateArg(c), utcArg(c), houseArg(c, letter), '-emos', '-head'];
+      const { stdout, stderr } = runSwetestOrExit(swetestPath, argv, label);
+
+      // Raw streams go to the untracked staging dir FIRST so a failing call
+      // still leaves its evidence on disk for local inspection.
+      const stdoutFile = `case-${c.id}-${system}.stdout.txt`;
+      const stderrFile = `case-${c.id}-${system}.stderr.txt`;
+      writeFileSync(join(stagingDir, stdoutFile), stdout, 'utf8');
+      writeFileSync(join(stagingDir, stderrFile), stderr, 'utf8');
+
+      // Fail-closed: for quadrant systems, refuse output that mentions a
+      // silent Porphyry fallback (swetest does this at circumpolar
+      // latitudes) — on EITHER stream.
+      if (
+        (system === 'placidus' || system === 'koch') &&
+        /porphyry/i.test(`${stdout}\n${stderr}`)
+      ) {
+        process.stdout.write(
+          `[FAIL] swetest silently fell back to Porphyry for ${label}; ` +
+            'this sample cannot be used for a quadrant-system golden.\n',
+        );
+        process.exit(1);
+      }
+      // Any error-looking stderr aborts, whatever the exit code said.
+      if (/error|warning|invalid|cannot/i.test(stderr)) {
+        process.stdout.write(
+          `[FAIL] swetest wrote an error-looking message on stderr for ${label} ` +
+            `(see ${stderrFile} in the staging directory).\n`,
+        );
+        process.exit(1);
+      }
+
+      manifest.calls.push({
+        caseId: c.id,
+        system,
+        argv,
+        argvSha256: sha256(JSON.stringify(argv)),
+        stdoutFile,
+        stdoutSha256: sha256(stdout),
+        stderrFile,
+        stderrSha256: sha256(stderr),
+      });
+      systems[system] = parseSwetestHouses(stdout, label);
+    }
+    draft.cases.push({
+      id: c.id,
+      description: c.description,
+      utcIso,
+      latDeg: c.latDeg,
+      lonEastDeg: c.lonEastDeg,
+      systems,
+    });
+  }
+
+  writeFileSync(
+    join(stagingDir, 'manifest.json'),
+    `${JSON.stringify(manifest, null, 2)}\n`,
+    'utf8',
+  );
+  writeFileSync(
+    join(stagingDir, 'draft-fixture.json'),
+    `${JSON.stringify(draft, null, 2)}\n`,
+    'utf8',
+  );
+
+  // Atomic publish: only a COMPLETE capture ever becomes .tmp/house-golden-raw/.
+  // A pre-existing directory is renamed aside (never deleted, never merged).
+  if (existsSync(finalDir)) {
+    renameSync(finalDir, join(tmpRoot, `house-golden-raw.replaced-${stamp}`));
+  }
+  renameSync(stagingDir, finalDir);
+
+  process.stdout.write(
+    `[OK] captured ${manifest.calls.length} swetest invocations into .tmp/house-golden-raw/\n` +
+      '     Review draft-fixture.json + manifest.json, then hand them to the\n' +
+      '     populate step (see packages/western/goldens/README.md).\n',
+  );
+}
+
+main();
diff --git a/tools/swetest-parse.test.ts b/tools/swetest-parse.test.ts
new file mode 100644
index 0000000..2877783
--- /dev/null
+++ b/tools/swetest-parse.test.ts
@@ -0,0 +1,167 @@
+// Fully OFFLINE unit tests for the strict swetest output parser. Every input
+// below is a SYNTHETIC string written by hand — no real external tool output
+// is referenced, stored or replayed here.
+import { describe, expect, it } from 'vitest';
+import { parseSwetestAngle, parseSwetestHouses } from './swetest-parse.ts';
+
+describe('parseSwetestAngle', () => {
+  it('parses a DMS field to full precision (official -house shape)', () => {
+    expect(parseSwetestAngle("93°10'50.7734")).toBeCloseTo(93 + 10 / 60 + 50.7734 / 3600, 9);
+  });
+
+  it('parses a DMS field with a space before the seconds', () => {
+    expect(parseSwetestAngle("94°45' 1.3614")).toBeCloseTo(94 + 45 / 60 + 1.3614 / 3600, 9);
+  });
+
+  it('parses plain decimal degrees', () => {
+    expect(parseSwetestAngle('123.4567890')).toBeCloseTo(123.456789, 9);
+    expect(parseSwetestAngle('0')).toBe(0);
+  });
+
+  it('accepts the top of the valid range but rejects 360 itself', () => {
+    expect(parseSwetestAngle("359°59'59.999")).toBeLessThan(360);
+    expect(() => parseSwetestAngle("360°00'00.0")).toThrow();
+    expect(() => parseSwetestAngle('361.5')).toThrow();
+  });
+
+  it('rejects incomplete DMS fields (missing minutes or seconds)', () => {
+    expect(() => parseSwetestAngle('93°')).toThrow();
+    expect(() => parseSwetestAngle("93°10'")).toThrow();
+  });
+
+  it('rejects garbage, signs and empty input', () => {
+    expect(() => parseSwetestAngle('abc')).toThrow();
+    expect(() => parseSwetestAngle("93°10'5x.3")).toThrow();
+    expect(() => parseSwetestAngle('-5.0')).toThrow();
+    expect(() => parseSwetestAngle('')).toThrow();
+    expect(() => parseSwetestAngle('   ')).toThrow();
+  });
+
+  it('rejects out-of-range minutes and seconds components', () => {
+    expect(() => parseSwetestAngle("93°61'10.0")).toThrow();
+    expect(() => parseSwetestAngle("93°10'75.0")).toThrow();
+  });
+
+  it('rejects partial matches — the whole field must be consumed', () => {
+    expect(() => parseSwetestAngle("93°10'50.7734 junk")).toThrow();
+    expect(() => parseSwetestAngle('123.456 extra')).toThrow();
+  });
+
+  it('never echoes the raw field content in error messages', () => {
+    for (const bad of ["93°10'50.7734 junk", 'abc', '-5.0', "93°61'10.0"]) {
+      let message = '';
+      try {
+        parseSwetestAngle(bad, 'ctx');
+      } catch (e) {
+        message = (e as Error).message;
+      }
+      expect(message).not.toBe('');
+      expect(message).not.toContain(bad);
+    }
+  });
+});
+
+/**
+ * Build a synthetic, fully-populated TWO-COLUMN swetest -house stdout.
+ * Column 1 mixes DMS and decimal forms; column 2 is always a valid DMS
+ * lexeme (including one with an internal space before the seconds) whose
+ * value must never leak into the parsed result.
+ */
+function syntheticStdout(omit?: 'house7' | 'Ascendant' | 'MC'): string {
+  const lines: string[] = [];
+  for (let i = 1; i <= 12; i++) {
+    if (omit === 'house7' && i === 7) continue;
+    // Alternate DMS and decimal forms in column 1 to exercise both branches.
+    const base = (i * 30 + 3) % 360;
+    const col1 = i % 2 === 0 ? `${base}.5000000` : `${base}°15'30.0000`;
+    // One second column with an internal space before the seconds.
+    const col2 = i === 3 ? "94°45' 1.3614" : "12°34'56.7890";
+    lines.push(`house ${i}  ${col1}  ${col2}`);
+  }
+  if (omit !== 'Ascendant') lines.push("Ascendant  93°10'50.7734   8°15'20.0000");
+  if (omit !== 'MC') lines.push("MC         1.2345678   88°59'59.0000");
+  lines.push("ARMC       359°59'59.999   0°01'02.0000");
+  lines.push('Vertex     123.0000000'); // recognised-but-unused label
+  return `${lines.join('\n')}\n`;
+}
+
+describe('parseSwetestHouses', () => {
+  it('parses a complete two-column synthetic output (first column only enters the result)', () => {
+    const r = parseSwetestHouses(syntheticStdout(), 'synthetic/full');
+    expect(r.cusps).toHaveLength(12);
+    expect(r.cusps[0]).toBeCloseTo(33 + 15 / 60 + 30 / 3600, 9); // house 1 col1: 33°15'30.0000
+    expect(r.cusps[1]).toBeCloseTo(63.5, 9); // house 2 col1: 63.5000000
+    expect(r.cusps[2]).toBeCloseTo(93 + 15 / 60 + 30 / 3600, 9); // house 3 col1 (col2 has internal space)
+    expect(r.ascendant).toBeCloseTo(93 + 10 / 60 + 50.7734 / 3600, 9);
+    expect(r.mc).toBeCloseTo(1.2345678, 9);
+    expect(r.armc).toBeCloseTo(359 + 59 / 60 + 59.999 / 3600, 9);
+  });
+
+  it('rejects a house line missing its second column', () => {
+    const bad = syntheticStdout().replace(
+      "house 1  33°15'30.0000  12°34'56.7890",
+      "house 1  33°15'30.0000",
+    );
+    expect(() => parseSwetestHouses(bad, 'synthetic/one-col')).toThrow(/malformed two-column/);
+  });
+
+  it('rejects a house line with a third column', () => {
+    const bad = syntheticStdout().replace(
+      "house 1  33°15'30.0000  12°34'56.7890",
+      "house 1  33°15'30.0000  12°34'56.7890  7°08'09.0000",
+    );
+    expect(() => parseSwetestHouses(bad, 'synthetic/three-col')).toThrow(/malformed two-column/);
+  });
+
+  it('rejects a garbled second column', () => {
+    const bad = syntheticStdout().replace(
+      "house 1  33°15'30.0000  12°34'56.7890",
+      "house 1  33°15'30.0000  garbage",
+    );
+    expect(() => parseSwetestHouses(bad, 'synthetic/garbled-col2')).toThrow(/malformed two-column/);
+  });
+
+  it('rejects an incomplete DMS second column', () => {
+    const bad = syntheticStdout().replace(
+      "house 1  33°15'30.0000  12°34'56.7890",
+      "house 1  33°15'30.0000  94°45'",
+    );
+    expect(() => parseSwetestHouses(bad, 'synthetic/incomplete-col2')).toThrow(
+      /malformed two-column/,
+    );
+  });
+
+  it('rejects output with a missing house cusp', () => {
+    expect(() => parseSwetestHouses(syntheticStdout('house7'), 'synthetic/no-h7')).toThrow(
+      /missing house cusps 7/,
+    );
+  });
+
+  it('rejects output with a missing Ascendant or MC', () => {
+    expect(() => parseSwetestHouses(syntheticStdout('Ascendant'), 'synthetic/no-asc')).toThrow(
+      /missing Ascendant/,
+    );
+    expect(() => parseSwetestHouses(syntheticStdout('MC'), 'synthetic/no-mc')).toThrow(
+      /missing MC/,
+    );
+  });
+
+  it('rejects a malformed first-column value inside otherwise valid output', () => {
+    const bad = syntheticStdout().replace("house 1  33°15'30.0000", 'house 1  33°garbled');
+    expect(() => parseSwetestHouses(bad, 'synthetic/garbled')).toThrow();
+  });
+
+  it('never embeds raw line content in error messages', () => {
+    const sentinel = "33°15'30.0000GARBLEDSENTINEL";
+    const bad = syntheticStdout().replace("house 1  33°15'30.0000", `house 1  ${sentinel}`);
+    let message = '';
+    try {
+      parseSwetestHouses(bad, 'synthetic/sentinel');
+    } catch (e) {
+      message = (e as Error).message;
+    }
+    expect(message).not.toBe('');
+    expect(message).not.toContain(sentinel);
+    expect(message).not.toContain('GARBLEDSENTINEL');
+  });
+});
diff --git a/tools/swetest-parse.ts b/tools/swetest-parse.ts
new file mode 100644
index 0000000..77f499c
--- /dev/null
+++ b/tools/swetest-parse.ts
@@ -0,0 +1,170 @@
+/**
+ * Strict parser for Swiss Ephemeris `swetest -house` output.
+ *
+ * Pure module: no I/O, no environment access, no side effects — imported by
+ * both the one-time generator (tools/generate-house-golden.ts) and its fully
+ * OFFLINE unit tests (tools/swetest-parse.test.ts).
+ *
+ * Fail-closed by design: every numeric field must be consumed IN FULL (no
+ * partial matches), and every thrown error is structural only — it never
+ * echoes raw external output back, so nothing from a swetest run can leak
+ * into tracked logs via error messages.
+ */
+
+/** swetest DMS field, e.g. `93°10'50.7734` or `94°45' 1.3614` (space before seconds). */
+const DMS_RE = /^(\d{1,3})°\s*(\d{1,2})'\s*(\d{1,2}(?:\.\d+)?)"?$/;
+/** Plain decimal-degree field, e.g. `123.4567890`. */
+const DECIMAL_RE = /^\d{1,3}(?:\.\d+)?$/;
+
+// Non-anchored lexemes for splitting the TWO-COLUMN swetest line shape.
+// A DMS field may contain an internal space before the seconds, so columns
+// cannot be split on whitespace — the anchored two-column regex below
+// separates them by lexical shape (with backtracking), and its ^…$ anchors
+// reject a missing second column, a third column and any trailing garbage.
+const DMS_LEX = /\d{1,3}°\s*\d{1,2}'\s*\d{1,2}(?:\.\d+)?"?/;
+const FIELD_LEX = new RegExp(`(?:${DMS_LEX.source}|\\d{1,3}(?:\\.\\d+)?)`);
+const TWO_COL_RE = new RegExp(`^(${FIELD_LEX.source})\\s+(${DMS_LEX.source})$`);
+
+/**
+ * Parse a single swetest angle field into decimal degrees.
+ *
+ * Accepts exactly two shapes — DMS (`D°M'S[.frac]["]`) or decimal degrees —
+ * anchored over the WHOLE trimmed field. Anything else (missing minutes or
+ * seconds, stray characters, signs, trailing garbage, empty input) throws.
+ * The result must lie in [0, 360).
+ */
+export function parseSwetestAngle(field: string, context = 'angle'): number {
+  const trimmed = field.trim();
+  if (trimmed === '') {
+    throw new Error(`empty angle field (${context})`);
+  }
+
+  let value: number;
+  const dms = DMS_RE.exec(trimmed);
+  if (dms) {
+    const deg = Number(dms[1]);
+    const min = Number(dms[2]);
+    const sec = Number(dms[3]);
+    if (min >= 60) {
+      throw new Error(`minutes out of range (${context})`);
+    }
+    if (sec >= 60) {
+      throw new Error(`seconds out of range (${context})`);
+    }
+    value = deg + min / 60 + sec / 3600;
+  } else if (DECIMAL_RE.test(trimmed)) {
+    value = Number(trimmed);
+  } else {
+    throw new Error(`malformed angle field (${context})`);
+  }
+
+  if (!Number.isFinite(value) || value < 0 || value >= 360) {
+    throw new Error(`angle out of [0,360) range (${context})`);
+  }
+  return value;
+}
+
+export interface ParsedHouse {
+  cusps: number[]; // index 0 = house 1 ... index 11 = house 12
+  ascendant: number;
+  mc: number;
+  armc: number | null;
+}
+
+/**
+ * Split a recognised line's remainder into its two columns and return the
+ * parsed FIRST column. Column 1 must be a strictly valid DMS or decimal
+ * angle in [0,360) (re-checked by parseSwetestAngle's full-consumption
+ * contract) and is the value we keep. Column 2 must be present and fully
+ * match the swetest DMS lexeme, but is deliberately NOT captured as a golden
+ * value. Anything else — missing second column, a third column, trailing
+ * garbage, a garbled or incomplete second column — is rejected. The error
+ * stays structural: no raw external content is echoed.
+ */
+function parseTwoColumnValue(rest: string, where: string): number {
+  const m = TWO_COL_RE.exec(rest.trim());
+  if (!m) {
+    throw new Error(`malformed two-column line (${where})`);
+  }
+  return parseSwetestAngle(m[1]!, where);
+}
+
+/**
+ * Parse full swetest -house output. Standard lines are TWO-COLUMN (with
+ * -head suppressing the header):
+ *   house  1  93°10'50.7734  <second DMS column>
+ *   ...
+ *   house 12  ...           ...
+ *   Ascendant  ...          ...
+ *   MC         ...          ...
+ *   ARMC       ...          ...
+ * The remainder after each recognised label must match the two-column shape
+ * exactly; only the first column enters the result. Errors carry only the
+ * caller-supplied context, the 1-based line number and structural facts —
+ * never raw line content.
+ */
+export function parseSwetestHouses(stdout: string, context: string): ParsedHouse {
+  const cusps: (number | undefined)[] = new Array(12).fill(undefined);
+  let ascendant: number | undefined;
+  let mc: number | undefined;
+  let armc: number | null = null;
+
+  const lines = stdout.split(/\r?\n/);
+  for (let n = 0; n < lines.length; n++) {
+    const line = lines[n]!.trim();
+    const where = `${context} line ${n + 1}`;
+    if (line === '') continue;
+
+    const h = /^house\s+(\d{1,2})\s+(.+)$/i.exec(line);
+    if (h) {
+      const idx = Number(h[1]) - 1;
+      if (idx < 0 || idx > 11) {
+        throw new Error(`house number out of range (${where})`);
+      }
+      if (cusps[idx] !== undefined) {
+        throw new Error(`duplicate house ${idx + 1} line (${where})`);
+      }
+      cusps[idx] = parseTwoColumnValue(h[2]!, where);
+      continue;
+    }
+    const asc = /^Ascendant\s+(.+)$/i.exec(line);
+    if (asc) {
+      if (ascendant !== undefined) {
+        throw new Error(`duplicate Ascendant line (${where})`);
+      }
+      ascendant = parseTwoColumnValue(asc[1]!, where);
+      continue;
+    }
+    const armcM = /^ARMC\s+(.+)$/i.exec(line);
+    if (armcM) {
+      if (armc !== null) {
+        throw new Error(`duplicate ARMC line (${where})`);
+      }
+      armc = parseTwoColumnValue(armcM[1]!, where);
+      continue;
+    }
+    const mcM = /^MC\s+(.+)$/i.exec(line);
+    if (mcM) {
+      if (mc !== undefined) {
+        throw new Error(`duplicate MC line (${where})`);
+      }
+      mc = parseTwoColumnValue(mcM[1]!, where);
+      continue;
+    }
+    // Vertex / equat. Asc. / co-Asc. / polar Asc. etc — recognised but unused.
+  }
+
+  const missing = cusps
+    .map((v, i) => (v === undefined ? i + 1 : null))
+    .filter((x): x is number => x !== null);
+  if (missing.length > 0) {
+    throw new Error(`missing house cusps ${missing.join(',')} (${context})`);
+  }
+  if (ascendant === undefined) {
+    throw new Error(`missing Ascendant (${context})`);
+  }
+  if (mc === undefined) {
+    throw new Error(`missing MC (${context})`);
+  }
+  return { cusps: cusps as number[], ascendant, mc, armc };
+}