feat: run review phases in parallel or in sequence behind the phases input

.github/workflows/self_review.yml

@@ -54,3 +54,4 @@ jobs:
           openrouter_api_key: ${{ secrets.OPENROUTER_KEY }}
           model: ${{ vars.OPENROUTER_MODEL || 'anthropic/claude-sonnet-4-6' }}
           request_timeout_seconds: ${{ vars.UMM_REQUEST_TIMEOUT_SECONDS }}
+          phases: ${{ vars.UMM_PHASES }}

AGENTS.md

@@ -25,7 +25,7 @@ src/
   openrouter/              # OpenRouter I/O: @openrouter/sdk wrapper, per-attempt deadline, structured-output retry ladder, cost summary
   diff/                    # pure transforms over parse-diff output
   context/                 # workspace I/O: conventions file, changed files, import-trace scan, doc-mention scan, priority docs
-  review/                  # pure review logic: finding schema, phases, prompt, non-finding filter, unknown-file filter, path normalization, selection, comment mapping, title similarity, context notes, summary
+  review/                  # pure review logic: finding schema, phases + stage dispatch, prompt, non-finding filter, unknown-file filter, cross-phase merge, path normalization, selection, comment mapping, title similarity, context notes, summary
   orchestrate.ts           # pipeline + createPromptedGenerateFindings — fully testable with stub clients
 ```
 
@@ -188,9 +188,19 @@ files. Prefer SDK-provided types over redefining shapes.
 ## Review instruction authoring
 
 The bot's system-prompt instructions live in `src/review/phases.ts`
-(dimension constants + reporting rules) and `src/review/prompt.ts`
-(identity/scope, proof-of-work, severity rubric, output discipline). When
-writing or updating a review instruction, follow this formula — each
+(dimension constants, the per-phase pass-scope line, reporting rules, and
+the phase groups each `phases` mode dispatches) and `src/review/prompt.ts`
+(identity/scope, proof-of-work, severity rubric, output discipline).
+
+**Phase/stage mechanics:** a phase is one model call carrying a set of
+review dimensions. A stage groups the phases that run concurrently; stages
+run in order, and each later stage sees the earlier stages' findings.
+`combined` = 1 stage, 1 phase; `parallel` = 1 stage, 3 phases;
+`sequential` = 3 stages, 3 phases (1 each). The dispatch stack is
+`runStages` → `runStage` → `runPhase` in `src/review/run-stages.ts`;
+cross-phase finding collapse lives in `src/review/merge-phase-findings.ts`.
+
+When writing or updating a review instruction, follow this formula — each
 element is here because its absence measurably cost findings in live runs:
 
 - **Trigger, not preference.** Action + condition + boundary: "when you see

action.yml

@@ -37,7 +37,7 @@ inputs:
     required: false
     default: AGENTS.md
   phases:
-    description: "Review phases to run. V1 supports: combined"
+    description: "How the review dimensions are dispatched: combined (one model call carrying every dimension) | parallel (three focused calls at once — each reads deeper than the single call; wall clock is the slowest of the three and prompt tokens roughly triple) | sequential (the same three calls in order, each seeing the earlier findings). Empty = combined, so workflows can wire an unset repo variable directly"
     required: false
     default: combined
   context_budget_tokens:
@@ -93,7 +93,7 @@ outputs:
   review_url:
     description: URL of the submitted review; empty when no review was posted
   model_used:
-    description: Model that produced the accepted response
+    description: Model(s) that produced the accepted responses, comma-separated when phases were routed to different models
   skipped_reason:
     description: Non-empty when the review was skipped (e.g. diff too large)
 

src/__tests__/config.test.ts

@@ -85,6 +85,19 @@ describe("parseConfig", () => {
     expect(config.requestTimeoutSeconds).toBe(900)
   })
 
+  it("falls back to combined for an empty phases", () => {
+    const config = parseConfig(makeRawInputs({ phases: "" }))
+
+    expect(config.phases).toBe("combined")
+  })
+
+  it("passes phases through as a string for domain validation", () => {
+    // Value validation lives in review/phases.ts resolveStages
+    const config = parseConfig(makeRawInputs({ phases: "everything" }))
+
+    expect(config.phases).toBe("everything")
+  })
+
   it("rejects a zero request_timeout_seconds", () => {
     expect(() =>
       parseConfig(makeRawInputs({ requestTimeoutSeconds: "0" })),

src/__tests__/logger.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it, onTestFinished, vi } from "vitest"
-import { createLogger } from "../logger.js"
+import { createLogger, describeError } from "../logger.js"
 
 type WrittenLine = Record<string, unknown>
 
@@ -250,3 +250,17 @@ describe("createLogger", () => {
     expect(lines[1]?.sessionId).toBe("generated-later")
   })
 })
+
+describe("describeError", () => {
+  it("formats an Error as [Name]: message", () => {
+    const error = new TypeError("value is not a function")
+
+    expect(describeError(error)).toBe("[TypeError]: value is not a function")
+  })
+
+  it("stringifies a non-Error value", () => {
+    expect(describeError("plain string")).toBe("plain string")
+    expect(describeError(42)).toBe("42")
+    expect(describeError(null)).toBe("null")
+  })
+})