feat(compound-engineering): settings schema, getters, docs (U9)

Add settingsSchema (default session provider/model, enabled stages, sync
reconcile-on-hooks toggle, reconcile cadence hint) aligned across manifest.json
and the runtime manifest, with typed getters. Wire the consumed getters:
orchestrator passes defaultProvider/defaultModelId into sessions and rejects
disabled stages; hooks gate their reconcile drain on reconcileOnHooks. Add the
plugin README and docs/plugins/compound-engineering.md documenting the hub,
interactive sessions, work bridge, and the sync ownership model.

reconcileIntervalMinutes is exposed as an operator cadence hint but not yet
consumed (no host scheduler; reconcile is on-demand by design).

docs/plugins/compound-engineering.md

@@ -0,0 +1,99 @@
+# Compound Engineering Plugin
+
+A dedicated dashboard surface for the compound-engineering (CE) workflow — an
+artifact hub, interactive `ce-*` skill sessions, a work→board bridge, and
+event-driven bidirectional sync. It runs alongside Fusion's native pipeline.
+
+## Install
+
+1. Open **Settings → Plugins → Fusion Plugins**.
+2. In **Bundled Plugins**, click **Install** for **Compound Engineering**.
+3. Enable the plugin if it is not already started.
+
+When installed and enabled, the plugin registers the **Compound Engineering**
+dashboard view destination and installs its bundled `ce-*` skills into a
+plugin-local, discoverable directory (never a global `~/.claude/skills` path).
+
+## Dashboard view
+
+The Compound Engineering view is registered as a primary plugin destination
+(`viewId: "compound-engineering"`).
+
+It provides:
+- An **artifact hub** that discovers CE artifacts from conventional locations
+  (`STRATEGY.md`, `docs/ideation/`, `docs/brainstorms/`, plan docs, `docs/work/`,
+  `CONCEPTS.md`, `docs/solutions/`) grouped by stage, with explicit
+  empty / partial / error states.
+- Self-contained artifact previews read through plugin routes under
+  `/api/plugins/fusion-plugin-compound-engineering/`.
+- A **stage launcher** listing the registered, operator-enabled stages.
+
+## Sessions
+
+Each stage maps to a bundled skill via the stage registry
+(`{ stageId, skillId, artifactLocation, icon, label }`). Launching a stage starts
+an interactive agent session on the host's `createInteractiveAiSession` seam.
+
+The orchestrator streams `thinking`/`text` turns, surfaces a structured
+`question` (pausing in `awaiting_input`), accepts a structured answer, and on
+`complete` writes the artifact to the stage's conventional location. Lifecycle:
+`launching → active → awaiting_input → completed`, plus `error` and
+`interrupted`. Interrupt/error auto-saves progress and emits an observable event;
+sessions resume/retry back to their current question.
+
+Transport is polling (`GET /sessions/:id`) — plugin routes have no native
+server-push and no raw `EventSource` is used.
+
+HTTP endpoints (under `/api/plugins/fusion-plugin-compound-engineering/`):
+- `POST /sessions` → start a stage session
+- `POST /sessions/:id/answer` → answer the awaiting question
+- `POST /sessions/:id/resume` → resume an awaiting/interrupted session
+- `GET /sessions/:id` → current persisted session state (polling)
+- `GET /sessions` → list sessions (filter by status/stage)
+- `GET /sessions/:id/links` → the work→board pipeline-link records for a session
+
+## Sync model
+
+Two separate state machines are kept in sync, never merged:
+
+- **Board-task ownership** → the task `column`. The **board is authoritative for
+  task state**.
+- **CE-pipeline ownership** → `ce_pipeline_state.{currentStage, status}`. The
+  **CE flow is authoritative for artifact/pipeline content**.
+
+**Inbound:** `onTaskMoved` / `onTaskCompleted` hooks resolve the link and enqueue
+a sync signal under the 5s hook budget — no inline advancement.
+
+**Reconcile:** `reconcileCePipelines(ctx)` is a single on-demand sweep (not a
+poll loop). It drains the queue and independently re-derives transitions from
+live board state, so a dropped or never-enqueued event still converges.
+
+**Outbound:** when a pipeline advances to a stage that produces board work, the
+reconciler creates the next-stage board task and links it.
+
+**Conflict policy:** the reconciler only reads already-terminal board columns and
+only writes CE-owned fields plus a new board task, so the two writers never
+contend over the same cell.
+
+The work bridge tags every CE-originated board task (source `workflow_step` with
+CE markers in `sourceMetadata`) and records an authoritative pipeline-link row;
+created tasks then run the normal lifecycle untouched.
+
+## Settings
+
+Settings render under **Settings → Plugins → Compound Engineering**.
+
+**Sessions**
+- `defaultProvider` (string) — provider for CE interactive sessions; blank uses
+  the host default. Consumed by the orchestrator's factory call.
+- `defaultModelId` (string) — model within the provider; blank uses the host
+  default. Consumed by the orchestrator's factory call.
+- `enabledStages` (string[], default = full registry) — only these stage IDs may
+  be launched; the orchestrator rejects others.
+
+**Sync**
+- `reconcileOnHooks` (boolean, default `true`) — auto-fire the reconcile sweep
+  after task move/complete hooks. When off, the hook still enqueues so an
+  on-demand sweep converges later.
+- `reconcileIntervalMinutes` (number, default `15`) — cadence hint for an
+  on-demand refresh surface; not a continuous poll loop.