U4 substrate PR1: extract the git-evidence readers (19/19 bodies byte-identical, self-healing.ts -449)

[gsxdsm]

Based on main. PR1 of the substrate decomposition — deliberately small and boring.

Mechanical proof (the point of this PR)

Every moved body diffed against its pre-move text:

BLOCK                            KIND     DIFF-vs-ORIGINAL
  LandedTaskCommit               iface    EMPTY
  commitOwnedByTask              helper   EMPTY
  escapeRegex                    helper   EMPTY
  shellQuote                     helper   EMPTY
  parseShortstat                 helper   EMPTY
  findLandedTaskCommit           method   EMPTY
  findAlreadyMergedTaskCommit    method   EMPTY
  refreshRemoteBaseRef           method   EMPTY
  readCommitTaskOwnership        method   EMPTY
  branchHasNoUniqueDiff          method   EMPTY
  baseHasExplicitTaskOwnership   method   EMPTY
  foreignTipRejection            method   EMPTY
  branchTipForeignOwnership      method   EMPTY
  isCommitReachableFromBranch    method   EMPTY
  findWorktreePathForBranch      method   EMPTY
  repoBranchExists               method   EMPTY
  readShortstatForSha            method   EMPTY
  readLandedFilesForSha          method   EMPTY
  isBranchTipMisboundToTask      method   EMPTY

RESULT: 19/19 BYTE-IDENTICAL modulo the enumerated deviations; 0 differ.

No condition reordered, no signature changed, no rename, no inlining, no "while I am here" cleanup.

The premise needed correcting — the cheap lesson this cut was meant to buy

The brief described 13 pure functions. They are 13 private async methods closing over this.options, so nothing here is byte-identical in the strict sense. Three deviations were structurally unavoidable:

1. private → protected on the 14 methods and the options field — a subclass cannot call a private base member. One token per declaration.
2. Two type annotations rewritten: SelfHealingManager["readCommitTaskOwnership"] → the base class, since the original would be a circular import.
3. Four module-level helpers moved along and re-exported. Forced by direction — the new module must not import self-healing.ts, so everything the bodies call has to live beside them. execAsync and shellQuote are imported back because call sites remain.

The set is 14, not 13

foreignTipRejection had to come too, and it's what closes the cluster — it depends only on baseHasExplicitTaskOwnership and branchHasNoUniqueDiff, both already in the set. Without it the extraction isn't self-contained and this.options isn't the only external dependency.

Base class, not free functions — deliberately

Converting to free functions would change all 14 signatures: a behavior-adjacent edit riding inside a file move, which is exactly the combination that hid the last four safeguard regressions. An abstract base keeps this semantics, so every call site stays this.<method>(...) and every body is unchanged text.

Two pre-existing collisions, preserved exactly

• The detector module already exports a free findAlreadyMergedTaskCommit sharing a name with the protected method; inside the class body the bare identifier resolves to the import.
• SelfHealingOptions is declared in self-healing.ts, imported here type-only so it's erased at runtime and creates no module cycle.

Measured line delta — not an estimate

	lines
self-healing.ts	13,394 → 12,945 = −449
new module	+527 (454 moved verbatim, 73 scaffold)
NET	+78

Same shape as every consolidation in this program: the target file shrinks, the total grows slightly. At −449 for the first and safest cut, the remaining substrate cuts plausibly take self-healing.ts under 11k — but that is file-size reduction, not code reduction.

Verification

464 passed across three engine suites with the single known pre-existing archiveStaleDoneTasks failure; tsc clean; lint clean; merge gate green (299 + 10 + 71).

No changeset: @fusion/engine is private.

🤖 Generated with Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between 4819c26 and 4297254.

📒 Files selected for processing (2)

• packages/engine/src/self-healing-git-evidence.ts
• packages/engine/src/self-healing.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/u4-substrate-git-evidence

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[greptile-apps]

Greptile Summary

This PR extracts the git-evidence readers from the self-healing manager without changing their behavior.

• Adds SelfHealingGitEvidence, an abstract base class containing the relocated git and task-ownership readers.
• Moves and re-exports the associated helpers and evidence types.
• Updates SelfHealingManager to inherit the extracted implementation while preserving its constructor and call sites.

Confidence Score: 5/5

The PR appears safe to merge with no concrete behavioral, build, or security regressions identified.

The extracted methods retain their existing behavior, inherited call sites resolve correctly, the constructor initializes the new base class, and the reverse dependency is type-only and therefore absent at runtime.

Important Files Changed

Filename	Overview
packages/engine/src/self-healing-git-evidence.ts	Introduces the abstract git-evidence base class and relocates the existing readers and helpers without an identified behavioral regression.
packages/engine/src/self-healing.ts	Replaces local git-evidence implementations with inheritance from the extracted base while retaining compatible construction and method resolution.

Class Diagram

%%{init: {'theme': 'neutral'}}%%
classDiagram
    class SelfHealingGitEvidence {
        <<abstract>>
        #options: SelfHealingOptions
        #findLandedTaskCommit()
        #findAlreadyMergedTaskCommit()
        #branchTipForeignOwnership()
        #isBranchTipMisboundToTask()
    }
    class SelfHealingManager {
        -store: TaskStore
        #options: SelfHealingOptions
    }
    SelfHealingGitEvidence <|-- SelfHealingManager
    SelfHealingGitEvidence ..> AlreadyMergedDetector : delegates
    SelfHealingGitEvidence ..> Git : reads evidence

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