feat(gateway): carry intake technical depth down the chain + widen review coherence scope (#491)

Two structural issues flagged by the CEO:

1. Task technical-depth dilution — intake's rich analysis (file:line
   targets, code examples, rationale) was getting lost as it traveled
   umbrella -> root-subtask -> cell -> dev. The detail IS preserved in
   Task.description; the dilution was in delegation (PMs re-authoring)
   and the intake prompt not demanding depth.

   Fixes:
   - evidence_repo: ancestor_context_for_task walks the parent chain
     (cycle-guarded, depth-capped 16, desc-clipped 1500) and surfaces it
     as parent_context in the evidence payload, so a leaf dev finally
     sees the upstream intake analysis instead of a bare title.
   - evidence_builder: Task.description now rides in the payload;
     EvidencePayload gains description + parent_context (omit-when-empty
     so no null noise).
   - orchestrator: _description_body (capped 4000) injects the
     description into the dev spawn prompt + SessionStart briefing.
   - role prompts (main_pm/cell_pm/developer/prompter): teach pass-the-
     torch, don't-dim-it; prompter now demands file:line/code-examples
     in the_work/notes (reconciled with the no-code-level-ACs-on-roots
     rule). main_pm's brief-not-a-spec scoped: not-a-spec applies to the
     solution only, facts forward verbatim.

2. PR-review/QA scope too narrow — they only checked the AC checklist,
   not whether the change is coherent with project structure/intent.

   Fixes:
   - qa.md + pr_reviewer.md: Coherence & intent rule (intent via
     description+parent_context, coherence with project patterns,
     standards). Criterion-less major findings allowed for intent drift
     (Finding.criterion is optional).
   - parent_context + description wired into the gate/QA/inbound-PR
     evidence builders (fail-open, logged).

Skipped per YAGNI: a technical_spec JSONB column (detail is already in
description) and a criterion_kind enum (criterion is already optional).

All gates green: ruff, mypy (1152), pytest (12883 passed, 94.82% cov),
xenon, vulture, bandit, pip-audit, deptry, alembic, import-linter,
foundation-check.

Co-authored-by: Renn F <rennf93@users.noreply.github.com>

tests/unit/gateway/test_evidence_builder.py

@@ -444,3 +444,68 @@ class TestExtractPmReview:
         digest = build_task_handoff(t, [])
         assert digest is not None
         assert "pm_review" not in digest
+
+
+class TestDescriptionAndParentContext:
+    """The ask (description + upstream parent_context) now rides the evidence
+    payload and the task handoff so a freshly-claimed leaf receives the intake's
+    analysis instead of an empty handoff."""
+
+    def test_payload_omits_description_when_none(self) -> None:
+        """A descriptionless task must not emit ``description: null`` in every
+        evidence payload — omitted like the other noise-when-empty fields."""
+        t = _task()
+        ev = build_evidence_for_task(t, journal_highlights=[], files_changed=[])
+        assert "description" not in ev.as_dict()
+
+    def test_payload_carries_description_when_set(self) -> None:
+        t = _task()
+        t.description = "edit prompter.py:412 to thread task_id through"
+        ev = build_evidence_for_task(t, journal_highlights=[], files_changed=[])
+        assert (
+            ev.as_dict()["description"]
+            == "edit prompter.py:412 to thread task_id through"
+        )
+
+    def test_payload_carries_parent_context(self) -> None:
+        t = _task()
+        chain = [
+            {
+                "task_id": "p",
+                "depth": 1,
+                "title": "Root",
+                "description": "intake analysis",
+            }
+        ]
+        ev = build_evidence_for_task(
+            t, journal_highlights=[], files_changed=[], parent_context=chain
+        )
+        assert ev.as_dict()["parent_context"] == chain
+
+    def test_payload_omits_parent_context_when_empty(self) -> None:
+        t = _task()
+        ev = build_evidence_for_task(t, journal_highlights=[], files_changed=[])
+        assert "parent_context" not in ev.as_dict()
+
+    def test_handoff_carries_description_and_parent_context(self) -> None:
+        """A leaf with no commits/PR yet still gets a handoff when the spec
+        (description) or the upstream chain is present — the intake analysis
+        reaches the dev at claim time."""
+        t = _task(pr_number=None, pr_url=None, commits=[], dev_notes="")
+        t.description = "the ask: edit foo.py:10"
+        chain = [
+            {"task_id": "p", "depth": 1, "title": "Root", "description": "upstream"}
+        ]
+        handoff = build_task_handoff(t, [], parent_context=chain)
+        assert handoff is not None
+        assert handoff["description"] == "the ask: edit foo.py:10"
+        assert handoff["parent_context"] == chain
+
+    def test_handoff_none_when_no_spec_and_no_prior_work(self) -> None:
+        """A bare task with no spec, no commits, no PR, no findings, no upstream
+        chain still collapses to None — no empty handoff payload."""
+        t = _task(pr_number=None, pr_url=None, commits=[], dev_notes="")
+        t.commits = []  # _task's `commits or [...]` default would re-seed one
+        t.acceptance_criteria_status = []
+        # MagicMock auto-attrs make description a non-str -> _typed -> None.
+        assert build_task_handoff(t, []) is None