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, 49 insertions, 0 deletions

diff --git a/docs/superpowers/plans/2026-09-20-artifact-pipeline-implementation.md b/docs/superpowers/plans/2026-09-20-artifact-pipeline-implementation.md
new file mode 100644
index 0000000..e1cb4e6
--- /dev/null
+++ b/docs/superpowers/plans/2026-09-20-artifact-pipeline-implementation.md
@@ -0,0 +1,49 @@
+# Artifact Pipeline Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Complete the typed artifact pipeline from the shared contract through the Blender CLI, server SSE, and browser manifest link.
+
+**Architecture:** Keep `SomhairlesDream.Shared` as the wire contract, put deterministic artifact writing and Blender invocation in `SomhairlesDream.Modeling`, expose it through a thin CLI, and have the ASP.NET server run the same pipeline asynchronously. Preserve the existing replay store and UI path.
+
+**Tech Stack:** F#/.NET 8, ASP.NET Core minimal APIs, `System.Text.Json`, `System.Diagnostics.Process`, xUnit, Blender Python fixture.
+
+---
+
+### Task 1: Align contracts and lifecycle validation
+
+**Files:** `src/SomhairlesDream.Shared/Artifact.fs`, `src/SomhairlesDream.Modeling/Definitions.fs`, `src/SomhairlesDream.Server/Store.fs`, and the corresponding Shared/Modeling/Server tests.
+
+- [ ] Add checkpoint `TotalSteps` and serialize it as flat camel-case JSON.
+- [ ] Make design object IDs cumulative snapshots and require completion only after all ordered checkpoints.
+- [ ] Verify focused tests and keep legacy `RunStore` behavior unchanged.
+
+### Task 2: Implement the Blender bridge and CLI
+
+**Files:** `src/SomhairlesDream.Modeling/BlenderBridge.fs`, `src/SomhairlesDream.Cli/Program.fs`, `stage/blender/fixture.py`, project files, and CLI/Modeling tests.
+
+- [ ] Add a process bridge using `ProcessStartInfo.ArgumentList`, bounded to 120 seconds, with structured result/error handling, an explicit result file, and retained stdout/stderr logs.
+- [ ] Add the deterministic `bpy` fixture with step validation, object custom properties, GLB reimport verification, and optional PNG render.
+- [ ] Add CLI `run` and `verify` exit-code behavior and test fake-bridge/argument paths.
+
+### Task 3: Wire server execution and SSE
+
+**Files:** `src/SomhairlesDream.Server/Program.fs`, `src/SomhairlesDream.Server/Store.fs`, server project/tests.
+
+- [ ] Add the Modeling reference and launch the same pipeline in a background task.
+- [ ] Implement exact-run start, SSE, manifest, artifact, validation, conflict, and 404 responses.
+- [ ] Add one-second stale observation without changing lifecycle status.
+
+### Task 4: Update browser and solution wiring
+
+**Files:** `src/SomhairlesDream.Frontend/App.fs`, `public/index.html`, `public/App.js`, and `SomhairlesDream.sln`.
+
+- [ ] Start a selected run, subscribe to its exact SSE stream, and expose `artifact-manifest-link` only on completion.
+- [ ] Preserve replay behavior and the existing `Uint32BufferAttribute` mesh path.
+- [ ] Include Modeling and CLI projects in the solution.
+
+### Task 5: Verify and publish
+
+- [ ] Run all project tests and builds.
+- [ ] Run the real `bpy 5.0.1` integration and CLI verification, then server/browser checks.
+- [ ] Review status/diff, commit only scoped project files, publish to the authorized bare repository, and verify `git ls-remote` plus cgit.