Fix #2601: drop "One PR" opener from planner prompts; align both paths on slice-DAG

orchestrator/routes/pipelines.py

@@ -11105,11 +11105,12 @@ def _build_phase_prompt(
     elif phase == "plan":
         lines.extend(
             [
-                "Create a detailed implementation plan.",
-                "",
-                "**CRITICAL CONSTRAINT — One Issue = One Workflow = One PR.**",
-                "All tasks belong to a single pull request. Use phases and commits to",
-                "organise the work within that PR — do NOT propose multiple PRs.",
+                "Create a detailed implementation plan, decomposing the work into "
+                "slices per the slice-DAG guidance at the end of this section. The "
+                "implement-phase pipeline ships each slice as its own stacked PR. "
+                "A single-slice plan is fine when the work is cohesive; multi-slice "
+                "plans are required when an upstream refine-phase work-decomposition "
+                "HITL decision selected a multi-slice shape.",
                 "",
                 "Steps:",
                 "1. Review any prior analysis",
@@ -11166,13 +11167,45 @@ def _build_phase_prompt(
                 "",
                 *_YAML_TASKS_SAFETY_GUIDANCE,
                 "",
-                "Do NOT use a `pr_plan` key or propose multiple PRs.",
+                "Do NOT use a `pr_plan` key — slice packaging is owned by the "
+                "slice-DAG section below, not by an ad-hoc PR list.",
                 "",
                 "The `test_plan` field is **required** — describe both automated test "
                 "coverage and any manual verification steps. The `manual_steps` field "
                 "should list any pre-merge or post-merge actions required by the reviewer "
                 "or deployer; use an empty string if none.",
                 "",
+                # ----------------------------------------------------
+                # #2137 — slice-DAG planner guidance (mirrors the
+                # concurrent task_planner block; keep the two paths
+                # aligned so a refine-phase multi-slice HITL decision
+                # is honoured regardless of which planner runs).
+                # ----------------------------------------------------
+                "## Slice-DAG guidance (#2137)",
+                "",
+                "The implement-phase pipeline ships each plan **slice** (formerly "
+                "**phase**) as its own stacked PR. The plan you emit drives that "
+                "DAG; the rules below are mandatory.",
+                "",
+                "**Yaml key swap**: prefer the canonical ``slices:`` key in your "
+                "``# yaml-tasks`` block (the parser also accepts ``phases:`` for "
+                "backward compatibility). New plans should use ``slices:``.",
+                "",
+                "**Slice-sizing guidance (soft, advisory only)**: target ≤1,000 "
+                "LOC per slice where possible. The plan reviewer flags oversized "
+                "slices as advisory but does NOT reject on size.",
+                "",
+                "**Forest constraint (HARD)**: every slice must have at most ONE "
+                "DAG parent — the implement-phase pipeline ships every slice as a "
+                "stacked PR with exactly one base branch. Multi-parent slices "
+                "break the stacking invariant and are rejected at plan ingestion.",
+                "",
+                "**Auto-serialization rule for would-be multi-parent slices**: "
+                "when a slice would naturally have >1 parents, serialise the "
+                "upstream slices into a linear chain and record the chosen "
+                "ordering on the downstream slice's ``serialized_chain_order`` "
+                "field.",
+                "",
                 f"Write your plan to `{plan_path}`.",
                 "Commit and push the draft when done.",
                 "",
@@ -13031,11 +13064,13 @@ def _build_agent_prompt(
         draft_path = _get_draft_path("plan", issue_number=issue_number, pipeline_id=pipeline_id)
         lines.extend(
             [
-                "Decompose the architecture analysis into a single-PR implementation plan.",
-                "",
-                "**CRITICAL CONSTRAINT — One Issue = One Workflow = One PR.**",
-                "All tasks belong to a single pull request. Use phases and commits to",
-                "organise the work within that PR — do NOT propose multiple PRs.",
+                "Decompose the architecture analysis into a slice-DAG implementation "
+                "plan. The implement-phase pipeline ships each slice as its own "
+                "stacked PR — see the ``## Slice-DAG guidance (#2137)`` section below "
+                "for the slice-shaping rules. A single-slice plan is fine when the "
+                "work is cohesive; multi-slice plans are required when an upstream "
+                "refine-phase work-decomposition HITL decision selected a "
+                "multi-slice shape.",
                 "",
                 "Steps:",
                 "1. Review the architecture analysis from the ARCHITECT agent",
@@ -13094,7 +13129,8 @@ def _build_agent_prompt(
                 "",
                 *_YAML_TASKS_SAFETY_GUIDANCE,
                 "",
-                "Do NOT use a `pr_plan` key or propose multiple PRs.",
+                "Do NOT use a `pr_plan` key — slice packaging is owned by the "
+                "slice-DAG section below, not by an ad-hoc PR list.",
                 "",
                 "The `test_plan` field is **required** — describe both automated test "
                 "coverage and any manual verification steps. The `manual_steps` field "

orchestrator/tests/test_pipeline_prompts.py

@@ -3289,6 +3289,93 @@ def test_decomposition_guidance_lives_outside_template_fence(self):
             )
 
 
+class TestPlannerPromptSliceDagFraming:
+    """Planner prompts must not contradict slice-DAG decomposition (#2601).
+
+    Both planner paths — ``_build_phase_prompt(phase="plan")`` (sequential)
+    and ``_build_agent_prompt(role_value="task_planner")`` (concurrent) —
+    used to open with ``CRITICAL CONSTRAINT — One Issue = One Workflow =
+    One PR`` and a follow-on ``do NOT propose multiple PRs`` line. That
+    directly contradicts the slice-DAG guidance the concurrent path already
+    carried and silently turned multi-slice refine-phase HITL decisions
+    into dead letters. This class is a negative-regression suite: the
+    opener must not return, and the slice-DAG framing must remain.
+    """
+
+    @staticmethod
+    def _sequential_plan_prompt() -> str:
+        return _build_phase_prompt(
+            phase="plan",
+            pipeline_id="test-pipe",
+            pipeline_mode="issue",
+            prompt="Implement the change.",
+            issue_number=100,
+        )
+
+    @staticmethod
+    def _concurrent_planner_prompt() -> str:
+        return _build_agent_prompt(
+            role_value="task_planner",
+            phase="plan",
+            pipeline_id="test-pipe",
+            pipeline_mode="issue",
+            prompt="Implement the change.",
+            issue_number=100,
+            concurrent=True,
+        )
+
+    def test_sequential_plan_drops_one_pr_opener(self):
+        prompt = self._sequential_plan_prompt()
+        for needle in (
+            "CRITICAL CONSTRAINT",
+            "One Issue = One Workflow = One PR",
+            "do NOT propose multiple PRs",
+        ):
+            assert needle not in prompt, (
+                f"sequential planner still carries removed opener {needle!r} — "
+                "this contradicts slice-DAG decomposition (#2601)"
+            )
+
+    def test_concurrent_planner_drops_one_pr_opener(self):
+        prompt = self._concurrent_planner_prompt()
+        for needle in (
+            "CRITICAL CONSTRAINT",
+            "One Issue = One Workflow = One PR",
+            "do NOT propose multiple PRs",
+        ):
+            assert needle not in prompt, (
+                f"concurrent planner still carries removed opener {needle!r} — "
+                "this contradicts slice-DAG decomposition (#2601)"
+            )
+
+    def test_sequential_plan_includes_slice_dag_guidance(self):
+        prompt = self._sequential_plan_prompt()
+        for needle in (
+            "Slice-DAG guidance (#2137)",
+            "stacked PR",
+            "Forest constraint",
+            "serialized_chain_order",
+        ):
+            assert needle in prompt, (
+                f"sequential planner missing slice-DAG token {needle!r} — "
+                "the two planner paths must stay aligned (#2601)"
+            )
+
+    def test_concurrent_planner_includes_slice_dag_guidance(self):
+        prompt = self._concurrent_planner_prompt()
+        for needle in (
+            "Slice-DAG guidance (#2137)",
+            "stacked PR",
+            "Forest constraint",
+            "serialized_chain_order",
+        ):
+            assert needle in prompt, (
+                f"concurrent planner missing slice-DAG token {needle!r} — "
+                "removing the One-PR opener must not have dropped the "
+                "slice-DAG block (#2601)"
+            )
+
+
 class TestReviewerBrcPreamble:
     """Tests that reviewer agents receive BRC preamble in concurrent mode."""