FN-5767: wire workflow graph executor to legacy seams

Complete Phase 3 interpreter parity by routing workflow graph execution through legacy seam handlers.

- Simplify workflow IR schema and built-in coding workflow to seam-based v1 nodes/edges.
- Add workflow node handler layer with default legacy seam adapters and dedicated handler/parity tests.
- Update engine exports/executor behavior for conditional traversal, retries, outcome context, and parity assertions.
- Refresh core workflow IR tests/coverage for the new shape (including seam-stage expectations without triage) and remove obsolete schema fixture test.

Files changed:
 .changeset/fn-5767-interpreter-parity.md           |   5 +
 .github/actions/setup-node-pnpm/action.yml         |  41 +---
 docs/workflow-steps.md                             |  17 ++
 .../__tests__/builtin-coding-workflow-ir.test.ts   |  25 +--
 packages/core/src/__tests__/workflow-ir.test.ts    |  70 ------
 packages/core/src/builtin-coding-workflow-ir.ts    |  71 ++----
 packages/core/src/index.ts                         |  31 +--
 packages/core/src/workflow-ir-types.ts             |  91 +-------
 packages/core/src/workflow-ir.ts                   | 246 ++-------------------
 .../workflow-graph-executor-handlers.test.ts       | 201 +++++++++++++++++
 .../workflow-graph-executor-parity.test.ts         | 126 ++++++++---
 .../src/__tests__/workflow-node-handlers.test.ts   |  50 +++++
 packages/engine/src/index.ts                       |  16 +-
 packages/engine/src/workflow-graph-executor.ts     | 205 ++++++++++++-----
 packages/engine/src/workflow-node-handlers.ts      |  56 +++++
 15 files changed, 661 insertions(+), 590 deletions(-)

Fusion-Task-Id: FN-5767

Fusion-Task-Lineage: 0c68586e-2709-4521-a2ce-938ba1006ae0

.github/actions/setup-node-pnpm/action.yml

@@ -30,37 +30,16 @@ runs:
         cache: pnpm
         registry-url: ${{ inputs.registry-url }}
 
-    # Cache node_modules only for the exact pnpm-lock.yaml hash and Node/OS/arch tuple.
-    # runner.arch is essential: pnpm only installs the current platform's optional
-    # native deps (e.g. @rollup/rollup-linux-arm64-gnu), so an x64 cache restored on
-    # an arm64 runner (same runner.os) would be missing native binaries and break builds.
-    # github.job scopes the key per job: jobs sharing an OS/arch (e.g. the windows-x64
-    # CLI build and the Windows desktop build) would otherwise race on the same key and
-    # one would fail the post-job cache save ("unable to reserve cache ... another job
-    # may be creating this cache"). Per-job keys trade a little reuse for reliability.
-    # Intentionally no restore-keys fallback: partial restores can create inconsistent trees.
-    - name: Cache node_modules
-      id: node-modules-cache
-      if: ${{ inputs.skip-install != 'true' }}
-      uses: actions/cache@v4
-      with:
-        path: |
-          node_modules
-          **/node_modules
-          !**/.cache
-        key: node-modules-${{ github.job }}-${{ runner.os }}-${{ runner.arch }}-node${{ inputs.node-version }}-${{ hashFiles('pnpm-lock.yaml') }}
-
+    # Do NOT cache the linked node_modules tree. pnpm builds node_modules from
+    # symlinks/junctions into the content-addressable store, and actions/cache does
+    # not preserve Windows junctions across its tar/restore — a restored tree has
+    # broken peer links (e.g. @vitejs/plugin-react can't resolve its `vite` peer →
+    # ERR_MODULE_NOT_FOUND), which silently broke the Windows release build. The
+    # pnpm *store* is already cached by actions/setup-node above (`cache: pnpm`), so
+    # `pnpm install --frozen-lockfile` is fast with a warm store and relinks
+    # correctly per-OS/arch every time (also fixing the prior arch-key and per-job
+    # cache-race issues this node_modules cache was patched for).
     - name: Install dependencies
-      if: ${{ inputs.skip-install != 'true' && steps.node-modules-cache.outputs.cache-hit != 'true' }}
+      if: ${{ inputs.skip-install != 'true' }}
       shell: bash
       run: pnpm install ${{ inputs.install-args }}
-
-    - name: Verify restored node_modules cache integrity
-      if: ${{ inputs.skip-install != 'true' && steps.node-modules-cache.outputs.cache-hit == 'true' }}
-      shell: bash
-      run: |
-        test -f node_modules/.modules.yaml || {
-          echo "ERROR: node_modules cache hit but node_modules/.modules.yaml is missing"
-          exit 1
-        }
-        pnpm -v