refactor(plugin-sdk): make API baseline module-mergeable (#121842)

docs/.generated/README.md

@@ -7,7 +7,7 @@ snapshots remain local inspection artifacts.
 
 - `config-baseline.sha256` — hashes of config baseline JSON artifacts.
 - `config-baseline.counts.json` — maximum entry counts for each config baseline kind.
-- `plugin-sdk-api-baseline.jsonl` — one content-derived record per Plugin SDK module and export.
+- `plugin-sdk-api-baseline.jsonl` — one content hash per Plugin SDK module.
 - `sqlite-session-transcript-schema-baseline.sha256` — hash of the sessions/transcripts SQLite schema baseline.
 
 **Local only (gitignored):**
@@ -24,11 +24,11 @@ Do not edit any of these files by hand.
 - Validate Plugin SDK API contract manifest: `pnpm plugin-sdk:api:check`
 
 The Plugin SDK contract sorts modules by import specifier and exports by kind
-then name. Its line-delimited records keep concurrent changes to separate
-exports mergeable. Export records carry the normalized `declaration` and an
-explicit `closureHash` for surface-reachable repo declarations. Committed
-records omit source paths so file moves do not change the contract; origin
-`source` fields remain available in the local pretty JSON snapshot.
+then name. Each line hashes one module's normalized declarations and the
+surface-reachable declaration closure hashes, so changes to different modules
+do not rewrite shared aggregate records. Committed records omit source paths so
+file moves do not change the contract; origin `source` fields remain available
+in the local pretty JSON snapshot.
 
 - Regenerate SQLite sessions/transcripts schema baseline: `pnpm sqlite:sessions-schema:gen`
 - Validate SQLite sessions/transcripts schema baseline: `pnpm sqlite:sessions-schema:check`