feat(pipeline): add runnable artifact pipeline increment

[Change Nature]
- This commit adds the first runnable increment of the F# artifact
  pipeline: CLI, server, frontend bundle, stage fixture, and tests.
  It is feature work, not a bug fix.

[New Capability]
- CLI `run` executes the three-step Blender fixture through the process
  bridge and writes GLBs, step logs, events, and a manifest; `verify`
  validates a manifest without Blender.
- Server exposes run start, run-scoped SSE, artifact manifest/file
  routes, and serves the Fable frontend from its build output.
- Frontend starts runs, follows run-scoped SSE progress, and links the
  artifact manifest on completion.

[Implementation]
- Shared layer holds domain, run state, replay, and artifact contracts;
  Modeling holds the pipeline, 120s bridge timeout, and result-file
  protocol; stage/blender/fixture.py owns geometry in Python (bpy owns
  geometry, F# owns orchestration).
- Fable bundle is regenerated into public/ and copied by the server
  project; solution includes all projects with warnings-as-errors.
- README documents build, Fable, server, interpreter/env, fixture
  limitations, and current verification status.

[Impact]
- Verified: 40/40 solution tests pass; Release build 0 warnings/errors;
  real CLI run with bpy 5.0.1 produced 3 GLBs, 3 logs, and a
  verify-clean manifest; isolated-port server smoke flow succeeded.
- Not yet verified: browser end-to-end behavior and production
  fidelity. Artifacts and caches are gitignored.

1 files changed, 20 insertions, 12 deletions

diff --git a/docs/superpowers/specs/2026-09-20-artifact-pipeline-design.md b/docs/superpowers/specs/2026-09-20-artifact-pipeline-design.md
index 4fe314c..ab0fd6d 100644
--- a/docs/superpowers/specs/2026-09-20-artifact-pipeline-design.md
+++ b/docs/superpowers/specs/2026-09-20-artifact-pipeline-design.md
@@ -48,9 +48,9 @@ namespaced IDs such as `heritage.foundation` are valid.
   `checkpoint`, `heartbeat`, `complete`, or `fail`.
 - `ArtifactChange`: object ID, change kind, and human-readable summary.
 - `RenderArtifact`: relative PNG path, SHA-256, byte count, and export time.
-- `StepArtifact`: step metadata, immutable relative GLB path, SHA-256, byte
-  count, actual Blender export timestamp, source object IDs, verified object
-  IDs from GLB reimport, changes, and optional render.
+- `StepArtifact`: step metadata, immutable relative GLB path, retained process
+  log path, SHA-256, byte count, actual Blender export timestamp, source object
+  IDs, verified object IDs from GLB reimport, changes, and optional render.
 - `ArtifactManifest`: schema version, run IDs, lifecycle timestamps, Blender
   version, ordered step artifacts, and final status.
 
@@ -90,6 +90,10 @@ Each run is isolated at:
 .artifacts/<projectId>/<runId>/
   events.ndjson
   manifest.json
+  logs/
+    01-foundation.log
+    02-frame.log
+    03-cabin.log
   steps/
     01-foundation.glb
     02-frame.glb
@@ -111,10 +115,11 @@ status is `complete`. The `Complete` event is appended after the rename; a
 crash or event-log failure at that point leaves the manifest authoritative and
 is recovered as complete on the next inspection, without deleting or
 rewriting it. A manifest is never published if any required step fails before
-the commit point. `verify` recomputes all
-recorded hashes, checks paths stay inside the run directory, checks the source
-and verified object ID sets recorded by the bridge, checks timestamps, and
-rejects duplicate step paths. Reimport is performed by the real stage
+the commit point. `verify` recomputes all recorded hashes, checks retained
+process logs are present and non-empty, checks paths stay inside the run
+directory, checks the source and verified object ID sets recorded by the
+bridge, checks timestamps, and rejects duplicate step paths. Reimport is
+performed by the real stage
 integration command before the manifest is written; `verify` does not need
 Blender and validates the recorded proof plus the design's expected ID set.
 
@@ -140,15 +145,18 @@ The bridge protocol is fixed. The F# process invokes:
 
 ```text
 <python> stage/blender/fixture.py --step-id <id> --output <tmp.glb>
-  [--render-output <tmp.png>]
+  --result-output <tmp.result.json> [--render-output <tmp.png>]
 ```
 
 `<python>` comes from `--python` or `SOMHAIRLES_BPYTHON`; the default is
 `python3`. The script must import `bpy` and report version `>= 3.0.0`. Exit 0
-prints exactly one JSON result object containing `ok`, `blenderVersion`,
-`exportedAt`, `objectIds`, `verifiedObjectIds`, `glbBytes`, and optional
-`renderPath`/`renderedAt`. Exit 2 means invalid step or arguments, exit 3
-means missing/unsupported `bpy`, and exit 4 means export or render failure.
+writes exactly one JSON result object to `--result-output` containing `ok`,
+`blenderVersion`, `exportedAt`, `objectIds`, `verifiedObjectIds`, `glbBytes`,
+and optional `renderPath`/`renderedAt`. Standard output and standard error are
+diagnostic streams only; the bridge retains both in the step log so incidental
+Blender output cannot corrupt result parsing. Exit 2 means invalid step or
+arguments, exit 3 means missing/unsupported `bpy`, and exit 4 means export or
+render failure.
 The bridge timeout is 120 seconds per step. `exportedAt` is emitted by Python
 immediately after the successful GLB export; F# rejects a missing or non-UTC
 timestamp. `verifiedObjectIds` comes from reimporting the just-written GLB and