Overview / Motivation

Auto-filed by the workflow-fix-on-bug protocol from a workflow-fix candidate raised on task #1333 (emitting agent: experiment-implementer, 9a-ter free-analysis round).

Goal

Make the events.jsonl marker-append self-healing against a crash-truncated final line (seal a missing trailing newline before appending, with a warning).

Workflow gap

• Bug observed: a task.py post-marker invocation killed mid-append left an unterminated partial JSON line at the end of tasks/interpreting/1333/events.jsonl; the retry's O_APPEND write concatenated its row onto the partial, producing ONE merged unparseable line (parse error at char ~1680 = the partial's length) that every reader must skip (task.py readers warn+skip; no content lost, but the NEXT marker was corrupted by the PRIOR crash).
• Why it is a workflow gap: the marker-append helper in src/explore_persona_space/task_workflow.py never verifies the file ends with a newline before appending, so any crash-truncated final line silently corrupts the next marker instead of just itself.
• Confidence (emitter): medium
• verified-at-filing: grep -rn "SEEK_END|trailing newline|missing trailing" src/explore_persona_space/task_workflow.py -> 1 hit (line 3191, a docstring about fixture trailing newlines — no existing self-heal on the append path); the corrupted line is live at tasks/interpreting/1333/events.jsonl line ~152 as evidence (2026-07-15)

Proposed change (candidate diff sketch — refine in planning)

• self-heal a crash-truncated final line before appending (#1333 fu incident)

• if path.exists() and path.stat().st_size > 0:

• with open(path, "rb") as f:
  

•     f.seek(-1, os.SEEK_END)
  

•     if f.read(1) != b"\n":
  

•         logger.warning("events.jsonl missing trailing newline — sealing truncated line")
  

•         newline_prefix = b"\n"
  

  with open(path, "ab") as f:

• f.write(row_bytes)
  

• f.write(newline_prefix + row_bytes)
  

Scope / surfaces

• Primary target: src/explore_persona_space/task_workflow.py (the events append path; in-scope workflow surface despite the general src/ exclusion)
• Grep the workflow surface for other O_APPEND jsonl writers (grep -rln '"ab"' src/explore_persona_space/task_workflow.py scripts/) and apply the same seal where the same crash-concatenation class applies; list hits in the plan.

Constraints / invariants

• Workflow-surface only. scripts/workflow_lint.py --check-asks passes; ruff passes; tests pin the seal (append onto a truncated fixture produces two parseable lines).
• This session runs under EPM_WORKFLOW_FIX_SESSION=1 and carries a workflow_fix_target: Provenance line — recursion guard applies.

Provenance

• workflow_fix_target: src/explore_persona_space/task_workflow.py
• fingerprint: eb776453ca97

(Verbatim candidate block from the emitting agent's report is preserved in the origin_prompt.)