build(web): compile source WebEngine with local emsdk

docs/status/WBV2-P27-002.md

@@ -0,0 +1,10 @@
+# WBV2-P27-002 status
+
+- task: `WBV2-P27-002`; parent: `WBV2-P27-001`; status: `in_progress`
+- source prerequisite: `PASS`; Blender 5.2.0 `web_engine` compiled from `blender-5.2.0` with local Emscripten 3.1.69
+- compiled artifacts copied to `web/app/src/vendor/blender/` and `web/app/public/vendor/blender/`
+- application package rebuilt with `web_engine-C1wwLZyc.wasm` and `web-engine.worker-C3G0ZxMq.js`
+- build command exit: `0`; log: `tests/golden/WBV2-P27-002/source-build.log`
+- Chromium production receipt, malformed/transaction/persistence/determinism verification: `DEFERRED_BY_IMPLEMENTATION_FIRST_MODE`
+- inventory unchanged: `6900` total, `281` legacy completed, `6618` legacy pending, `290/6609` effective carried forward
+- nextTask remains `WBV2-P27-003` until deferred verification starts

docs/tasks/WBV2-P27-002.md

@@ -15,6 +15,8 @@ Run only new Chromium production behaviors with malformed, transaction and persi
 
 - Focused inventory: `tests/golden/WBV2-P0-002/parity-map.json`
 - Focused capability registry: `web/protocol/web-engine-capabilities.ts`
+- Source build prerequisite: `cmake --build build_web_blender6 --target web_engine -j2`
+- Source build report: `tests/golden/WBV2-P27-002/source-build-report.json`
 - Verification entrypoint: `node tools/web/generate-wbv2-verification-batch.mjs --task WBV2-P27-002 --write`
 
 ## 验收
@@ -23,6 +25,7 @@ Run only new Chromium production behaviors with malformed, transaction and persi
 - existing Blender/WASM/Chromium evidence is not rerun
 - malformed, unsupported, transaction, save/reopen and deterministic checks are required only for a new behavior
 - completion overlay remains unchanged until a complete one-to-one receipt exists
+- implementation-first mode permits the source build prerequisite while Chromium production execution remains deferred
 - `node tools/web/check-task-context.mjs --task WBV2-P27-002 --write`
 
 ## 交付与回滚