feat: add shadow LangGraph orchestrator runtime

docs/architecture/memind-orchestrator-boundary.md

@@ -54,6 +54,11 @@ Native selection.
 The initial workflow allowlist contains only `code-run-v1`. Ordinary chat and
 existing Goosed session traffic remain outside the Orchestrator path.
 
+Phase 2 implements only the `off` and `shadow` execution semantics. Although
+Canary and Active can be configured and evaluated by the control plane, the
+Portal does not hand execution ownership to LangGraph yet. This prevents an
+administrative configuration mistake from creating two task executors.
+
 ## Protocol
 
 The framework-neutral contracts are:
@@ -61,7 +66,7 @@ The framework-neutral contracts are:
 - `orchestrator-run-v1`
 - `orchestrator-event-v1`
 
-The eventual internal API is:
+The implemented internal API is:
 
 ```text
 POST /v1/runs
@@ -75,13 +80,38 @@ External state changes must use an idempotency key derived from run, graph
 version, node, and attempt. Graph state stores resource references and decisions,
 not API keys, large logs, binary artifacts, or absolute production paths.
 
+The Phase 2 graph has three deterministic nodes:
+
+```text
+validate_run -> build_plan -> finalize_run
+```
+
+It requires `policy.executionMode=observe-only` and
+`policy.sideEffectsAllowed=false`. It projects the Native executor boundary but
+cannot call Goosed, Aider, OpenHands, Tool Gateway, or the filesystem.
+
+## Failure isolation
+
+Portal invokes Shadow only after the product run and its `queued` event have
+been committed. The observation is scheduled without awaiting it. A timeout or
+failure:
+
+1. cannot reject or delay `createRun`;
+2. cannot mutate the Native run status;
+3. is projected as `workflow_shadow_failed`;
+4. remains removable by deleting the observer wiring and changing only the
+   service URL boundary.
+
+Successful observations are projected as `workflow_shadow_completed`; graph
+checkpoints stay in the Orchestrator-owned PostgreSQL database.
+
 ## Deployment evolution
 
-1. Local native Orchestrator process with a development checkpoint database.
-2. 103 shadow LaunchAgent; no production task claim.
-3. User-allowlisted code-run canary with Native rollback.
-4. Isolated Aider/OpenHands executor workers.
-5. Containerized Orchestrator in its own Compose project.
+1. Local native Orchestrator process with an explicit MemorySaver for debugging.
+2. Colima Compose with an isolated PostgreSQL checkpoint database.
+3. Approved server-side shadow service; no production task claim.
+4. User-allowlisted code-run canary with Native rollback.
+5. Isolated Aider/OpenHands executor workers.
 6. Move the same service contract to Linux or Kubernetes when horizontal scaling
    or independent ownership becomes necessary.