fix(gcp-to-aws): resume/recovery reliability — stale reuse, corrupt state, mid-flow read

migrate/plugins/migration-to-aws/skills/gcp-to-aws/SKILL.md

@@ -129,7 +129,11 @@ Generate phase additionally loads `references/shared/validate-artifacts.md` befo
 When reading `$MIGRATION_DIR/.phase-status.json`, validate before proceeding:
 
 1. **Multiple sessions**: If multiple directories exist under `.migration/`, list them with their phase status and ask: [A] Resume latest, [B] Start fresh, [C] Cancel.
-2. **Invalid JSON**: If `.phase-status.json` fails to parse, STOP. Output: "State file corrupted (invalid JSON). Delete the file and restart the current phase."
+2. **Invalid JSON**: If `.phase-status.json` fails to parse, do NOT delete it and do NOT restart from Discover — the phase artifacts on disk are the durable record of progress. Reconstruct instead:
+   1. Enumerate `$MIGRATION_DIR` and infer completed phases from artifacts: any of `gcp-resource-inventory.json` / `billing-profile.json` / `ai-workload-profile.json` → discover completed; `preferences.json` → clarify completed; `aws-design.json` / `aws-design-ai.json` / `aws-design-billing.json` → design completed; `estimation-*.json` → estimate completed (**partial-write check:** if `preferences.json` has an `ai_constraints` section — or `ai-workload-profile.json` / `aws-design-ai.json` is present — but `estimation-ai.json` is missing while another `estimation-*.json` exists, treat estimate as **incomplete**, not completed; propose resume at estimate); `generation-*.json` or `MIGRATION_GUIDE.md` → generate completed.
+   2. Present the inferred status to the user: "Your state file was corrupted, but I can see [phases] completed from the artifacts on disk. Resume at [next phase]? (Y/N)". **Confirmation is the safety net for residual ambiguity** (e.g. other partial writes the heuristic misses) — on N, the user picks the phase to resume.
+   3. On Y: rewrite `.phase-status.json` with the inferred phases marked `"completed"`, the next phase `"pending"`, `current_phase` set to it, and a fresh `last_updated`. Continue normally. On N: ask which phase to resume from and write that instead.
+      This is reconstruction of ground truth from artifacts, not artifact-patching to pass a gate — the handoff-gate prohibition does not apply to `.phase-status.json` recovery.
 3. **Unrecognized phase**: If `phases` object contains a phase not in {discover, clarify, design, estimate, workshop, generate, feedback}, STOP. Output: "Unrecognized phase: [value]. Valid phases: discover, clarify, design, estimate, workshop, generate, feedback."
 4. **Unrecognized status**: If any `phases.*` value is not in {pending, in_progress, completed}, STOP. Output: "Unrecognized status: [value]. Valid values: pending, in_progress, completed."
 5. **Invalid `current_phase`** (if present): If `current_phase` is not in {discover, clarify, design, estimate, generate, complete}, STOP. Output: "Unrecognized current_phase: [value]. Valid values: discover, clarify, design, estimate, generate, complete." (`workshop` and `feedback` are sidebars — never `current_phase`.)

migrate/plugins/migration-to-aws/skills/gcp-to-aws/references/phases/clarify/clarify-global.md

@@ -269,7 +269,7 @@ Default: B — `availability: "multi-az"`.
 
 **Database migration tooling notes:**
 
-- Read `preferences.json` → `design_constraints.db_size.value` (set by Q13b in `clarify-database.md`) to select the right tool. If absent, fall back to the size thresholds below.
+- Use the **in-flight resolved Q13b value** (`db_size` from Step 2 extraction, the confirmed Assumption Sheet, or `preferences-draft.json` — Q13b is defined in `clarify-database.md`) to select the right tool. Do NOT read `preferences.json` here: mid-Clarify it does not exist yet (it is written at Step 5), and on a re-run any file present is a prior run's stale answers. If Q13b is not yet resolved, fall back to the size thresholds below.
 - For PostgreSQL databases `db_size: "<10GB"` or unknown-small: **pg_dump/pg_restore** is sufficient.
 - For PostgreSQL databases `db_size: "10-100GB"` or `"100-500GB"`: **pgcopydb** offers parallel table copying and index rebuilding, significantly reducing migration time within the same maintenance window.
 - For PostgreSQL databases `db_size: ">500GB"`: **AWS DMS strongly recommended** regardless of maintenance window — single-pass export/import at this scale is high-risk.

migrate/plugins/migration-to-aws/skills/gcp-to-aws/references/phases/clarify/clarify.md

@@ -26,13 +26,30 @@ Check `$MIGRATION_DIR/` for existing state:
 
 **Case 1 — Completed preferences exist** (`preferences.json` present):
 
+**Compatibility check (run BEFORE offering reuse):** The existing file may predate the current flow, and the Completion Handoff Gate forbids patching artifacts to pass — so an incompatible file offered for reuse dead-ends at `GATE_FAIL`. Check:
+
+1. **Schema currency** — `metadata.clarify_mode` is present; every constraint has `value`, `chosen_by`, `prompt`, and `design_consequence`; every constraint with `chosen_by: "extracted"` or `"default"` has a `source` field; `design_constraints.cpu_architecture` is present when compute resources exist in the current inventory.
+2. **Discovery match** — the file's `metadata.discovery_artifacts` is consistent with what exists in `$MIGRATION_DIR` now: if `ai-workload-profile.json` exists but the file has no `ai_constraints` (or the reverse), or the inventory has database/compute resources whose required constraints (`availability`, `db_size`) are absent, the file is stale relative to current discovery.
+
+**If both pass**, offer:
+
 > "I found existing migration preferences from a previous run. Would you like to:"
 >
 > A) Re-use these preferences and skip questions
 > B) Start fresh and re-answer all questions
 
 - If A: Run Step 2 item 6 only (BigQuery detection) on current discovery artifacts. If `bigquery_present` is **true**, output the Step 4 **BigQuery / deferred analytics** advisory block once (even though questions are skipped), then skip to Validation Checklist with the existing `preferences.json`.
-- If B: delete `preferences.json`, continue to Step 1.
+- If B: rename `preferences.json` to `preferences-superseded.json` (do not delete — prior answers are unrecoverable otherwise), continue to Step 1.
+
+**If either check fails**, do NOT offer plain reuse — it would fail the gate. Instead:
+
+> "I found preferences from a previous run, but they predate the current flow (missing: [list]). Would you like to:"
+>
+> A) Keep your previous answers where they're still valid — I'll confirm them on the assumption sheet and only ask what's new or missing
+> B) Start fresh and re-answer all questions
+
+- If A: rename the old file to `preferences-superseded.json`, seed the wizard from it — carry each still-valid constraint value forward with its original `chosen_by` (backfilling `prompt`/`design_consequence`/`source` from the current catalog), treat missing constraints as unresolved — and continue to Step 1 (the wizard fills the gaps; carried-forward values appear on the Assumption Sheet for confirmation).
+- If B: rename to `preferences-superseded.json`, continue to Step 1.
 
 **Case 2 — Draft preferences exist** (`preferences-draft.json` present, no `preferences.json`):
 
@@ -747,7 +764,7 @@ Full schema and constraint catalog: `references/shared/schema-preferences.md`.
 15. `ai_constraints.ai_framework` is an array (Q14 is select-all-that-apply). If auto-detected, `chosen_by` is `"extracted"` with `source`.
 16. `metadata.clarify_mode` is one of `"wizard"`, `"full"`, `"fast_path"`, `"simple_hybrid"`.
 
-After writing `preferences.json`, delete `$MIGRATION_DIR/preferences-draft.json` if it exists.
+After writing `preferences.json`, delete `$MIGRATION_DIR/preferences-draft.json` and `$MIGRATION_DIR/preferences-superseded.json` if they exist (the superseded backup has served its purpose once a new complete file exists).
 
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