fix(ci): split the structured session-tabs sync and give static analysis mobile types

The local structured session-tabs sync module outgrew the 300-line cap once it
took on generation fencing, so split it along its real seams instead of raising
the cap: the generation/cursor fence, snapshot projection, snapshot apply,
inventory refresh, and the subscription loop. The original path stays as a
barrel so no importer moves.

Repoint the host-session-mirror settle census at the apply module, which owns
two receipts now — the snapshot it mirrors in, and the toggle-off teardown that
retracts what it published. The teardown receipt is named rather than anonymous
so the pin says which direction it settles.

The changed-code quality gate lints mobile files and resolves their types from
mobile/node_modules, but mobile is a separate pnpm project that the root install
never populates, so every mobile type degraded to an `error` type and the gate
reported phantom findings. Install mobile dependencies in static analysis when
the diff touches mobile, gated on a new classifier output.

.github/workflows/pr.yml

@@ -28,6 +28,7 @@ jobs:
     outputs:
       should_run: ${{ steps.filter.outputs.should_run }}
       native_cache_changed: ${{ steps.filter.outputs.native_cache_changed }}
+      mobile_dependencies: ${{ steps.filter.outputs.mobile_dependencies }}
       static_analysis: ${{ steps.filter.outputs.static_analysis }}
       typecheck: ${{ steps.filter.outputs.typecheck }}
       git_compatibility: ${{ steps.filter.outputs.git_compatibility }}
@@ -95,6 +96,15 @@ jobs:
       - name: Enforce type-aware code-quality baseline
         run: pnpm run audit:code-quality:type-aware
 
+      # Why: the changed-code gate lints mobile files too, and its type-aware pass
+      # resolves types from mobile/node_modules. Mobile is a separate pnpm project,
+      # so the root install above leaves it empty and every mobile type degrades to
+      # an `error` type — reported as phantom findings against the changed lines.
+      - name: Install mobile dependencies
+        if: needs.code_paths.outputs.mobile_dependencies == 'true'
+        working-directory: mobile
+        run: pnpm install --frozen-lockfile
+
       - name: Enforce changed-code quality
         run: pnpm run check:code-quality:changed -- "${{ github.event.pull_request.base.sha }}"