Merge main: adopt FN-5902 lazy assertion linkage in shared runFeatureValidation

- runFeatureValidation now lazy-ensures a linked assertion (FN-5902) instead
  of the removed zero-assertion auto-pass, for both task-completion and the
  stranded-feature recovery path
- CONCEPTS.md: union of main's Merge-lifecycle cluster and this branch's
  Missions clusters; Contract Assertion entry updated for FN-5902 semantics
- AGENTS.md: take main's docs/solutions + CONCEPTS.md pointer wording

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CONCEPTS.md

@@ -2,12 +2,12 @@
 
 Shared domain vocabulary for this project — entities, named processes, and status concepts with project-specific meaning. Seeded with core domain vocabulary, then accretes as ce-compound and ce-compound-refresh process learnings; direct edits are fine. Glossary only, not a spec or catch-all.
 
-## Relationships
+## Missions
+
+### Relationships
 
 A Mission owns an ordered list of Milestones; a Milestone owns an ordered list of Slices; a Slice owns a set of Features. Status rolls **up**, not down: a Slice's status is derived from its Features, a Milestone's from its Slices, and a Mission's from its Milestones. Autopilot acts at the Slice boundary — it advances a Mission by activating the next Slice once the current one is complete.
 
-## Missions
-
 ### Mission
 A unit of autonomous, multi-step work the system plans and then drives to completion on its own, decomposed into Milestones. A Mission may run under Autopilot or be advanced manually.
 
@@ -29,10 +29,39 @@ A Feature auto-generated from a failed Validator Run to carry the remediation wo
 The named process that watches an active Mission and advances it — activating the next pending Slice once the current Slice completes — while tracking its own watching/activating lifecycle and handling retries. When Autopilot is not watching a Mission, slice advancement falls back to a compatibility path.
 
 ### Contract Assertion
-A checkable acceptance criterion linked to a Feature that an AI validator judges to decide whether the Feature is genuinely done. A Feature with no linked assertions auto-passes; a Feature with assertions counts toward Slice completion only after a passing Validator Run.
+A checkable acceptance criterion linked to a Feature that an AI validator judges to decide whether the Feature is genuinely done. Every Feature is validator-evaluated — a Feature missing an assertion has one lazily linked before validation — and counts toward Slice completion only after a passing Validator Run.
 
 ### Validator Run
 A single execution of the AI judge that evaluates a Feature's Contract Assertions and yields a pass, fail, blocked, or error outcome. The validator is read-only — it inspects the implementation and records a verdict, creating no board task and editing no code. A run left running after its owner disappears is reaped to a terminal error state.
 
 ### loop state
 A Feature's position in the execution loop (being implemented, awaiting or undergoing validation, awaiting a fix, passed, or blocked), distinct from its board status. Logic that gates on loop state must treat it as possibly stale and possibly contradictory with status — a Feature can be marked done while its loop state was never advanced past implementing.
+
+## Merge lifecycle
+
+### Task
+The core board entity: a unit of work that moves through columns (triage, todo, in-progress, in-review, done, archived) and is executed by agents. A Task carries its own per-task settings that can override project-level defaults.
+
+### Auto-merge
+The named process that automatically lands a completed Task's branch onto its merge target once the Task reaches In-review and passes its merge blockers. Gated twice: a project-level setting enables it globally, and each Task may carry an explicit per-task override.
+
+The per-task override takes precedence in both directions: an explicit per-task enable proceeds even when the global setting is off, and an explicit per-task disable routes the merge to Manual-required even when the global setting is on. Trigger-layer gates (enqueue, Self-healing sweeps) must evaluate additively — global on lets everything through for downstream routing; global off admits only explicit per-task enables — rather than collapsing the override to a single effective value, which would starve Manual-required routing.
+
+### In-review
+The Task status column between execution and completion: work is done and the branch awaits merging. An In-review Task either auto-merges, waits for a human merge (PR-based/manual flow), or surfaces a stall diagnostic when it sits unprocessed longer than expected. Tasks not eligible for Auto-merge processing intentionally remain In-review until a human acts — recovery sweeps must not move them.
+
+### Merge queue
+The ordered line of In-review Tasks awaiting Auto-merge, with a single merge active at a time. Tasks enter only through trigger gates (engine startup sweep, periodic retry, unpause, and the moved-to-review fast path); a Task filtered out at a gate is invisible to the merger regardless of its own settings.
+
+### Manual-required
+The merge-request state for a Task whose merge needs an explicit human go-ahead — typically a Task with auto-merge explicitly disabled under a globally-enabled project. Reaching this state requires the Task to flow through the Merge queue trigger gates; upstream filtering that excludes such Tasks strands them In-review instead of parking them here.
+
+### Self-healing sweep
+A recurring background scan that detects and repairs stuck Task states — stalled In-review Tasks, confirmed merges never finalized, ghost or limbo states, exhausted retries. Sweeps respect the same Auto-merge eligibility as the Merge queue: they may inspect any Task but mutate only those eligible for auto-merge processing.
+
+### Shared branch group
+A set of Tasks integrating into a common shared branch instead of each merging straight to the project's default branch. Member integration (task branch → shared branch) is a soft pre-integration step exempt from the global auto-merge gate; promotion (shared branch → default branch) is gated separately.
+
+## Flagged ambiguities
+
+- "Merging" a shared-branch-group Task had been used for both member integration and group promotion — these are distinct steps with independent gating and must not be conflated.