fix(prompt-hook): skip unsafe roots during subproject down-scan (#1454) (#1812)

Reuse unsafeIndexRootReason before scanning indexed subprojects so stray manifests at home or broader roots cannot inject unrelated context. Preserve workspace adoption for #964.

Validation: four new regressions fail before the guard and pass after it; 48 relevant tests and npm run build pass. Confirmed the real os.homedir() leak before and after the fix with fixture cleanup.

Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>

CHANGELOG.md

@@ -141,6 +141,8 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 #### MCP / indexing
 
+- The prompt hook no longer injects unrelated projects when run from your home directory or a broader directory containing a stray workspace manifest. (#1454)
+
 - Indexing now succeeds when Node.js's SQLite lacks FTS5, with search falling back to name and fuzzy matching; thanks @aniruddhaadak80. (#1532)
 
 - `codegraph_explore` now makes clear that suggested call counts are advisory, so agents keep exploring when an answer is incomplete; thanks @rongbc. (#1504, #1570)