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Bug: history-shadow.ts has read-modify-write race condition (data loss) #479

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#480
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Bug: history-shadow.ts has read-modify-write race condition (data loss)#479
#480
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bugSomething isn't workinggo:needs-researchNeeds investigationnext-upPriority queue — next issues to worksquadSquad triage inbox — Lead will assign to a member

Description

@diberry
diberry
opened on Mar 20, 2026

@bradygaster — Found during SquadState PRD research.

Bug

\\history-shadow.ts\\ uses a read-modify-write pattern (\
eadFile → regex insert → writeFile\) with no locking. Two concurrent agents appending to the same \\history.md\\ will cause last-write-wins data loss.

How to reproduce

  1. Two agents write to the same agent's history.md simultaneously
  2. Agent A reads history.md (version 1)
  3. Agent B reads history.md (version 1)
  4. Agent A writes history.md (version 2 — includes A's changes)
  5. Agent B writes history.md (version 2 — includes B's changes but NOT A's)
  6. Agent A's changes are silently lost

Impact

This is a data loss bug in production today, not a theoretical concern. It affects any scenario where multiple agents or Scribe update the same history file concurrently.

Found by

Kaylee's edge case analysis during SquadState PRD research (19 edge cases audited, this was #1 highest risk).

Recommended fix

The planned SquadState abstraction will fix this by making write atomicity a contract requirement. Short-term mitigation: use the inbox/drop-box pattern for history writes (same as decisions), or add file locking.

cc @diberry

Activity

  1. diberry
    added a commit that references this issue on Mar 20, 2026

    fix: resolve read-modify-write race in history-shadow.ts

    266efa4

  2. bradygaster commented on Mar 22, 2026

    @bradygaster
    bradygaster
    on Mar 22, 2026
    Collaborator

    ⚠️ Flight triage: Data loss in history-shadow.ts read-modify-write pattern is production-critical. Routing: EECOM (core runtime) + RETRO (concurrency safety). Mitigation path: StorageProvider abstraction (#481) enforces atomic writes.

  3. bradygaster
    added
    squadSquad triage inbox — Lead will assign to a member
    squad:eecom
    squad:retro
    bugSomething isn't working
    on Mar 22, 2026
  4. github-actions
    added
    squad:fido
    go:needs-researchNeeds investigation
    on Mar 22, 2026

  5. github-actions commented on Mar 22, 2026

    @github-actions
    github-actionsBot
    on Mar 22, 2026 – with GitHub Actions
    Contributor

    📋 Assigned to EECOM (Core Dev)

    Issue: #479 — Bug: history-shadow.ts has read-modify-write race condition (data loss)

    EECOM will pick this up in the next Copilot session.

    For Copilot coding agent: If enabled, this issue will be worked automatically.
    Otherwise, start a Copilot session and say:
    EECOM, work on issue #479

  6. github-actions commented on Mar 22, 2026

    @github-actions
    github-actionsBot
    on Mar 22, 2026 – with GitHub Actions
    Contributor

    🏗️ Squad Triage — Flight (Lead)

    Issue: #479 — Bug: history-shadow.ts has read-modify-write race condition (data loss)
    Assigned to: FIDO (Quality Owner)
    Reason: Issue relates to testing/quality work

    @copilot evaluation: 🔴 Not suitable — issue involves work outside the coding agent's capability profile.

    Team roster:

    • Flight (Lead) → label: squad:flight
    • Procedures (Prompt Engineer) → label: squad:procedures
    • EECOM (Core Dev) → label: squad:eecom
    • FIDO (Quality Owner) → label: squad:fido
    • PAO (DevRel) → label: squad:pao
    • CAPCOM (SDK Expert) → label: squad:capcom
    • CONTROL (TypeScript Engineer) → label: squad:control
    • Surgeon (Release Manager) → label: squad:surgeon
    • Booster (CI/CD Engineer) → label: squad:booster
    • GNC (Node.js Runtime) → label: squad:gnc
    • Network (Distribution) → label: squad:network
    • RETRO (Security) → label: squad:retro
    • INCO (CLI UX & Visual Design) → label: squad:inco
    • GUIDO (VS Code Extension) → label: squad:guido
    • Telemetry (Aspire & Observability) → label: squad:telemetry
    • VOX (REPL & Interactive Shell) → label: squad:vox
    • DSKY (TUI Engineer) → label: squad:dsky
    • Sims (E2E Test Engineer) → label: squad:sims
    • Handbook (SDK Usability) → label: squad:handbook
    • Ralph (Work Monitor) → label: squad:ralph
    • @copilot (Coding Agent) → label: squad:copilot

    To reassign, remove the current squad:* label and add the correct one.

  7. github-actions commented on Mar 22, 2026

    @github-actions
    github-actionsBot
    on Mar 22, 2026 – with GitHub Actions
    Contributor

    📋 Assigned to RETRO (Security)

    Issue: #479 — Bug: history-shadow.ts has read-modify-write race condition (data loss)

    RETRO will pick this up in the next Copilot session.

    For Copilot coding agent: If enabled, this issue will be worked automatically.
    Otherwise, start a Copilot session and say:
    RETRO, work on issue #479

  8. bradygaster
    added
    next-upPriority queue — next issues to work
    on Mar 22, 2026
  9. bradygaster
    added a commit that references this issue on Mar 22, 2026

    fix: resolve read-modify-write race in history-shadow.ts

    ea7f4d9
  10. bradygaster
    closed this as completedin #480on Mar 22, 2026
  11. bradygaster
    added 2 commits that reference this issue on Mar 22, 2026

    fix: resolve read-modify-write race in history-shadow.ts (github#480)

    dfa513a

    docs(ai-team): Cross-agent triage updates + history initialization

    7c00ab7
  12. diberry
    added 2 commits that reference this issue on Mar 24, 2026

    refactor(agents): migrate history-shadow.ts to StorageProvider

    f9e0a7f

    refactor(agents): migrate history-shadow.ts to StorageProvider

    d906509
  13. chrislomonico
    added a commit that references this issue on Mar 26, 2026

    feat: smarter work division with multi-agent dispatch (github#342) (g…

    9b7db2a
  14. bradygaster
    removed
    squad:eecom
    squad:fido
    squad:retro
    on Sep 11, 2026
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