feat: planner overseer session advisor (OMP advisor parity) (#2082)

## Summary

Adds a **session advisor** to the planner overseer so Fusion can review
live executor transcripts the way [oh-my-pi’s
advisor](https://github.com/can1357/oh-my-pi/tree/main/packages/coding-agent/src/advisor)
does — without replacing the existing lifecycle supervisor (stage watch,
retry, merge confirmation, human-control withhold).

### What ships

- **Emission guard** (`OverseerEmissionGuard`) — content-free phrase
filter, session dedupe with severity-rank escalation, one accept per
advisor update
- **Session delta runtime** — queues agent-log deltas, drains through an
advisor agent, drops backlog after 3 failures
- **Session advisor service** — model gate, level matrix (`observe` /
`steer` / `autonomous`), human-control re-check at inject,
`[session-advisor]` steering comments
- **OVERSEER.md / WATCHDOG.md** discovery for project review priorities
- **AgentLogger `onEntriesFlushed`** + poll-backed agent-log cursor for
durable deltas
- Workflow settings: `plannerOverseerAdvisorProvider` +
`plannerOverseerAdvisorModelId` (both required; empty = soft-disabled
for cost safety)
- Docs + changeset

### What does not ship (deferred)

- Multi-advisor YAML roster, mutating advisor tools, reviewer/merger
shadowing, true tool-abort interrupt

### Plan

`docs/plans/2026-07-13-001-feat-overseer-advisor-parity-plan.md`

## Enablement

1. Set workflow **Session advisor model provider** + **Session advisor
model id**
2. Oversight level `observe` (log only), `steer`, or `autonomous`
(inject)
3. Optional: add `OVERSEER.md` or `WATCHDOG.md` in the project

## Test plan

- [x] `pnpm --filter @fusion/core exec vitest run
src/__tests__/overseer-emission-guard.test.ts`
- [x] `pnpm --filter @fusion/engine exec vitest run` overseer-* unit
tests (21 tests)
- [x] Related planner-overseer / intervention regression tests
- [x] `@fusion/engine` + `@fusion/core` typecheck
- [ ] Manual: configure advisor model, run an executor task, confirm
`[session-advisor]` inject + timeline metadata when concern is raised

## Residual Review Findings

None from autofix pass (log-cursor ordering fix already committed).


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Added an off-by-default “session advisor” that can review live
execution activity and provide severity-based guidance.
* Added project and per-task controls to enable it, including a default
enable switch and Quick Add / Task Detail toggles.
* Enhanced advisor prompting by discovering and incorporating
`OVERSEER.md`/`WATCHDOG.md` review files.
* **Documentation**
* Added architecture and settings documentation for the new
session-advisor parity behavior.
* **Bug Fixes**
* Improved fail-soft handling so advisor behavior won’t disrupt
execution.
  * Fixed concurrent PostgreSQL migration startup failures.
* **Tests**
* Added coverage for advice parsing, emission guarding, runtime
behavior, and watchdog discovery.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/dashboard/app/api/legacy.ts

@@ -476,6 +476,7 @@ export async function createTask(
     baseBranch,
     branchSelection,
     githubTracking,
+    sessionAdvisorEnabled,
     acknowledgedDuplicates,
     bypassDuplicateCheck,
   } = input;
@@ -514,6 +515,7 @@ export async function createTask(
       baseBranch,
       branchSelection,
       githubTracking,
+      sessionAdvisorEnabled,
       acknowledgedDuplicates,
       bypassDuplicateCheck,
     }),
@@ -572,6 +574,8 @@ export function updateTask(
     validatorThinkingLevel?: string | null;
     planningThinkingLevel?: string | null;
     plannerOversightLevel?: "off" | "observe" | "steer" | "autonomous" | null;
+    /** FNXC:PlannerOversight 2026-07-14-18:11: boolean override or null to inherit project default. */
+    sessionAdvisorEnabled?: boolean | null;
     reviewLevel?: number | null;
     executionMode?: "standard" | "fast" | null;
     noCommitsExpected?: boolean;