FN-8993: guard knowledge graph directory setting

Classify the knowledge graph output directory as an intentionally non-surfaced setting.

- Allowlist the CLI/engine-owned knowledgeGraphDir default with its rationale.
- Add regression coverage that preserves its Settings-description guard classification.

Files changed:
 .../settings-default-descriptions.test.tsx         | 33 ++++++++++++++++++++++
 1 file changed, 33 insertions(+)

Fusion-Task-Id: FN-8993

Fusion-Task-Lineage: 34d82e65-5d1d-4805-8630-f3393de8e998

Co-authored-by: Fusion (runfusion.ai) <noreply@runfusion.ai>

packages/dashboard/app/components/settings/sections/__tests__/settings-default-descriptions.test.tsx

@@ -387,6 +387,15 @@ const NOT_SURFACED_ALLOWLIST: Record<string, string> = {
   mergerCredentialInstanceId: "inline companion for the project merger model picker; unset inherits the provider default",
   mergerFallbackCredentialInstanceId: "inline companion for the project merger fallback model picker; unset inherits the provider default",
 
+  /*
+  FNXC:SettingsDefaults 2026-08-12-01:00:
+  FN-8993 classifies this CLI/engine-owned graph output path as not surfaced: it has
+  zero dashboard render sites and i18n keys, while only `fn knowledge-graph build`
+  and the memory-consolidation tick consume it. Operators can find its default in
+  docs/settings-reference.md and docs/knowledge-graph.md rather than a Settings field.
+  */
+  knowledgeGraphDir: "CLI/engine-owned knowledge-graph output directory (fn knowledge-graph build --dir); no Settings UI field renders it",
+
   // Internal/engine bookkeeping, session state, or reliability telemetry — not
   // rendered as a plain user-facing description field anywhere in Settings.
   globalPause: "engine-managed pause flag, not a plain description field",
@@ -659,6 +668,30 @@ describe("FN-7505 settings default-value description guard", () => {
     ).toEqual([]);
   });
 
+  /*
+  FNXC:SettingsDefaults 2026-08-12-01:00:
+  FN-8993 prevents knowledgeGraphDir from silently returning to the unaccounted-default
+  census failure. The CLI/engine-owned path belongs only in the not-surfaced allowlist.
+  */
+  it("pins FN-8993 knowledgeGraphDir as an allowlisted, non-Settings field", () => {
+    expect(
+      DEFAULT_SETTINGS,
+      "FN-8993 requires knowledgeGraphDir to remain a DEFAULT_SETTINGS key",
+    ).toHaveProperty("knowledgeGraphDir");
+    expect(
+      NOT_SURFACED_ALLOWLIST.knowledgeGraphDir,
+      "FN-8993 requires knowledgeGraphDir's non-empty not-surfaced allowlist reason",
+    ).toEqual(expect.any(String));
+    expect(
+      NOT_SURFACED_ALLOWLIST.knowledgeGraphDir,
+      "FN-8993 requires a non-empty knowledgeGraphDir allowlist reason",
+    ).not.toBe("");
+    expect(
+      SETTING_DESCRIPTION_KEYS,
+      "FN-8993 requires knowledgeGraphDir to stay out of SETTING_DESCRIPTION_KEYS",
+    ).not.toHaveProperty("knowledgeGraphDir");
+  });
+
   it("does not allowlist a key that is also mapped to a description (would mask real coverage gaps)", () => {
     const overlap = Object.keys(SETTING_DESCRIPTION_KEYS).filter((key) => key in NOT_SURFACED_ALLOWLIST);
     expect(overlap).toEqual([]);