diff --git a/packages/harness-omp/README.md b/packages/harness-omp/README.md
index 52c8073..be49e79 100644
--- a/packages/harness-omp/README.md
+++ b/packages/harness-omp/README.md
@@ -82,6 +82,14 @@ configuration for gateway/frontier models (delete the file or flip
 ignored, as are unknown keys (`generate_image` has no toggle and ships ~505
 tokens regardless).
 
+**`config/config.gateway-slim.yml`** — the measured middle ground (OPS-481,
+docs/eval/2026-07-09-code-mode-vs-omp-discovery.md): full default tool harness
+for gateway/frontier models, skills pinned to the shared allowlist. ~28.9k est
+tokens vs ~47k ambient (-38%); the skills block is the profile's only
+organically-growing cost (+1.7k/day observed from plugin sprawl). Regression
+gate: `tools/measure-context.sh --budget 31000 --settings
+config/config.gateway-slim.yml`.
+
 **`tools/measure-context.sh`** measures the real footprint: it runs `omp -p`
 against a localhost capture sink under a throwaway profile and prints the
 system/tools/skills breakdown. Run it on every pin bump
diff --git a/packages/harness-omp/config/config.gateway-slim.yml b/packages/harness-omp/config/config.gateway-slim.yml
new file mode 100644
index 0000000..f0ec28f
--- /dev/null
+++ b/packages/harness-omp/config/config.gateway-slim.yml
@@ -0,0 +1,32 @@
+# omp gateway-slim profile — full default TOOL harness, TRIMMED skill discovery.
+#
+# The measured middle ground (docs/eval/2026-07-09-code-mode-vs-omp-discovery.md,
+# OPS-481, row D): the gateway/frontier profile's skill auto-discovery block is
+# its largest and only ORGANICALLY-GROWING context cost (~16.5k est tokens and
+# +1.7k in a single day from ambient plugin growth). Pinning skills to the
+# shared allowlist — and nothing else — cut a live gateway profile from
+# ~47.0k to ~28.9k est tokens (-38%) with zero tool-availability change.
+#
+# vs the other presets:
+#   config.local.yml  — 32k-local-model profile: slims tools AND skills (~13k)
+#   this file         — gateway models (200k ctx): full tools, slim skills (~29k)
+#   no settings file  — omp defaults: full tools, ambient skills (~45k and growing)
+#
+# Install: copy to ~/.omp/agent/config.yml (never clobber live config).
+# Keys are NESTED maps — dotted keys are silently ignored (verified live).
+# The allowlist is CI-synced against packages/skills/ (tests/preset.test.ts).
+
+# --- role -> model mapping ---------------------------------------------------
+modelRoles:
+  default: llm/zai/GLM-5.2
+
+# --- skill discovery scoping (the ~16.5k lever; tools deliberately untouched) -
+skills:
+  includeSkills: [local-model-triage]
+  enablePiUser: true    # ~/.omp/agent/skills (omp-native user dir)
+  enablePiProject: true # .omp/skills in-repo
+  enableClaudeUser: false
+  enableClaudeProject: false
+  enableCodexUser: false
+  enableAgentsUser: false
+  enableAgentsProject: false
diff --git a/packages/harness-omp/tests/preset.test.ts b/packages/harness-omp/tests/preset.test.ts
index 6513e4b..5a41390 100644
--- a/packages/harness-omp/tests/preset.test.ts
+++ b/packages/harness-omp/tests/preset.test.ts
@@ -85,10 +85,41 @@ describe("config.local.yml", () => {
   });
 });
 
+describe("config.gateway-slim.yml", () => {
+  const GATEWAY_SLIM = readFileSync(join(PKG, "config/config.gateway-slim.yml"), "utf8");
+  const doc = Bun.YAML.parse(GATEWAY_SLIM) as Record<string, any>;
+
+  test("tools deliberately untouched (full gateway harness)", () => {
+    expect(doc.tools).toBeUndefined();
+  });
+
+  test("includeSkills allowlist stays in sync with packages/skills", () => {
+    const skillsDir = join(PKG, "../skills");
+    const shared = readdirSync(skillsDir, { withFileTypes: true })
+      .filter((e) => e.isDirectory() && existsSync(join(skillsDir, e.name, "SKILL.md")))
+      .map((e) => e.name)
+      .sort();
+    const allowlist = ([...(doc.skills?.includeSkills ?? [])] as string[]).sort();
+    expect(allowlist).toEqual(shared);
+  });
+
+  test("modelRoles point at models declared in models.yml", () => {
+    const models = Bun.YAML.parse(MODELS) as Record<string, any>;
+    const declared = new Set<string>();
+    for (const [prov, p] of Object.entries<any>(models.providers)) {
+      for (const m of p.models ?? []) declared.add(`${prov}/${m.id}`);
+    }
+    for (const [role, id] of Object.entries<string>(doc.modelRoles ?? {})) {
+      expect(declared.has(id), `${role}: ${id}`).toBeTrue();
+    }
+  });
+});
+
 describe("secretlessness", () => {
   test.each([
     ["models.yml", MODELS],
     ["config.local.yml", SETTINGS],
+    ["config.gateway-slim.yml", readFileSync(join(PKG, "config/config.gateway-slim.yml"), "utf8")],
   ])("%s carries no secret-shaped strings", (_name, text) => {
     for (const needle of SECRETY) expect(text).not.toInclude(needle);
   });