fix: Graceful Default-Init Skip in Non-Fab-Managed Repos

[sahil-noon]

Meta

Change ID	Type	Confidence	Plan	Review
irnt	fix	4.7/5.0	9/9 tasks, 20/20 acceptance ✓	✓ 1 cycle

Impact	+/−	Net
raw	+812 / −43	+769
true	+335 / −23	+312
└ impl	+111 / −18	+93
└ tests	+224 / −5	+219

_{excludes fab/, docs/ · generated by fab-kit v2.13.4}

Pipeline: intake ✓ → apply ✓ → review ✓ → hydrate ✓ → ship → review-pr

Summary

wt's default init script (fab sync) previously treated any non-fab-managed repo as a hard init failure (exit 7, kept-worktree banner, open-anyway prompt), even though the user never opted into that default. This change treats fab-kit's ExitNotManaged = 3 exit code as a graceful no-op when the init script is the built-in default, while an explicitly configured WORKTREE_INIT_SCRIPT still hard-fails on any non-zero exit.

Changes

• InitScriptPath() now signals provenance (isDefault) alongside the script string, so downstream logic can distinguish the built-in default from an explicit override
• Run-time skip classification: after fab sync exits non-zero, a default script + exit code 3 is treated as "does not apply" (stderr warning, exit 0, no banner, no prompt); all other cases keep today's hard-failure behavior
• Threaded isDefault through RunWorktreeSetup/RunWorktreeSetupWithObserver (crud.go) and wt init (cmd/wt/init.go), plus both wt create call sites (cmd/wt/create.go)
• Old fab-kit (pre-#471, exits 1) degrades to unchanged hard-fail behavior — no version detection or fallback probe
• Unit and integration test coverage for the classification helper, InitScriptPath provenance, and end-to-end wt create/wt init behavior via a stubbed fab binary
• Spec update to docs/specs/init-protocol.md documenting the new skip case and provenance-based lookup contract

[Copilot]

Pull request overview

This PR updates wt’s default worktree init behavior so that when the built-in default init script (fab sync) is run in a non-fab-managed repository and exits with fab-kit’s ExitNotManaged = 3, wt treats it as a graceful “does not apply” no-op (warning + exit 0) rather than an init failure (exit 7 + banner/prompt). It also threads “default vs explicit” provenance (isDefault) so only the built-in default gets this carve-out; explicitly configured init scripts still hard-fail on any non-zero exit.

Changes:

• InitScriptPath() now returns (script, isDefault) so callers can distinguish the built-in default from an explicit WORKTREE_INIT_SCRIPT override (even if the override equals "fab sync").
• Added a shared run-time classifier (DefaultNotApplicable) and canonical warning renderer (RenderDefaultSkipWarning) and applied them consistently in both init run sites (wt create and wt init).
• Added unit + integration tests (via stubbed fab) and updated specs/memory docs to document the new “default-not-applicable” skip semantics.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/internal/worktree/init.go	Adds exit-code classifier + shared skip-warning renderer for the default “fab sync” non-managed case.
src/internal/worktree/init_test.go	Unit tests for the classifier and warning renderer.
src/internal/worktree/crud.go	Threads isDefault into init runner and applies the skip classification in wt create’s init path.
src/internal/worktree/context.go	Changes InitScriptPath() to return both script and provenance (isDefault).
src/internal/worktree/context_test.go	Updates/adds provenance tests for InitScriptPath() (including explicit "fab sync").
src/cmd/wt/create.go	Passes (script, isDefault) through both init call sites.
src/cmd/wt/init.go	Applies the same skip classification in wt init, preserving TTY reclaim ordering.
src/cmd/wt/integration_test.go	Integration coverage using a stub fab to validate exit-3 skip vs exit-1 hard-fail and provenance gating.
docs/specs/init-protocol.md	Documents provenance reporting + the new run-time skip case and exit-3 carve-out.
docs/specs/cli-surface.md	Updates CLI exit-code semantics to reflect ExitInitFailed and the new non-failure skip outcomes.
docs/memory/wt-cli/init-failure-contract.md	Records the new default-not-applicable carve-out and shared-helper behavior.
docs/memory/wt-cli/create-output-phases.md	Notes the carve-out’s effect on wt init/wt create output/exit behavior.
fab/changes/260705-irnt-graceful-default-init-skip/intake.md	Captures requirements and design rationale for the change.
fab/changes/260705-irnt-graceful-default-init-skip/plan.md	Implementation plan and acceptance checklist for the change.
fab/changes/260705-irnt-graceful-default-init-skip/.status.yaml	Change metadata/status tracking.
fab/changes/260705-irnt-graceful-default-init-skip/.history.jsonl	Change execution history log.

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[sahil-noon]

Fixed — doc comment now says the exec error is wrapped via %w (not returned verbatim), while keeping the errors.As extraction guarantee. (6294663)