69 lines
3.7 KiB
Markdown
69 lines
3.7 KiB
Markdown
---
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name: parallel-worktree-path-hazard
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description: "\"Use when several agents edit the same repo in different git worktrees at once, or when an edit/read may have landed in the wrong checkout: which path forms bind where, how to detect with git -C status, and the repair protocol (cp + git show HEAD blob write-back) because git checkout/restore is policy-blocked in a shared workspace.\""
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---
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# Concurrent-worktree path hazard (shared repo, many agents)
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Measured 2026-10-18 on `serverAppConfigs` with two agents live at once. The
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failure is **silent**: the tool reports success, the diff looks right, and the
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change lives in a *different* worktree.
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## Which path form binds where
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- **Parent/top-level session**: a **relative** `path` resolves against the
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session CWD — its own worktree — never against the worktree named in the
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prompt. This is how a change meant for `wt-tts-trial-docs` landed in
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`wt-20261017-…`.
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- **Subagent**: an **absolute** path to its own assigned worktree can resolve
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into the parent's worktree when the same *relative* path exists there
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(`edit` twice onto `dankclaw/.env.example`). Its `write` with the same
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absolute path was fine — the bug is `edit`/`read` path resolution, not `write`.
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Rules that hold:
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1. A subagent passes paths as `../<its-worktree>/<rel>` (relative to the parent
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worktree) for `read` **and** `edit`; the parent passes **absolute** paths to
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any worktree that is not its own CWD.
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2. After every edit batch, prove the landing site, do not trust the tool's echo:
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`git -C <intended-worktree> status --short` must list the file. A file you
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edited that is missing from that list went somewhere else.
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3. Keep each work item on its own branch/worktree, and keep ONE integration
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owner (the parent) for shared files — `scripts/deploy-remote.sh`,
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`scripts/deploy-plan.py`, `tests/`, `serverAppConfigs-docs/index.md`,
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`AGENTS.md` are the collision hot spots in this repo. Never rebase a
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sibling's branch.
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## Repair protocol (no `git checkout`, no `git restore`)
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`git checkout -- <path>` and `git restore <path>` are **policy-blocked** in a
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shared workspace ("overwriting working-tree files … discards changes other
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concurrent agents rely on"). Unstaging (`git reset [<path>]`,
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`git restore --staged <path>`) is allowed but does not undo content. So:
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```bash
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F="path/with spaces if any"
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# 1. move the change to the worktree that should own it (both at the same base commit)
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cp "<wrong-wt>/$F" "<right-wt>/$F"
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# 2. undo in the wrong worktree by writing the committed blob back
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git -C "<wrong-wt>" show "HEAD:$F" | tee "<wrong-wt>/$F" > /dev/null
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# 3. prove both sides
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md5sum <(git -C "<wrong-wt>" show "HEAD:$F") "<wrong-wt>/$F" "<right-wt>/$F"
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git -C "<wrong-wt>" status --short # must be empty for that file
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git -C "<right-wt>" diff --stat # must show the intended delta
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```
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Never fix it blind: if the wrong worktree had its own uncommitted edits to that
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file, `cp`/blob-write-back would destroy them — check
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`git -C <wrong-wt> status --short` FIRST and reconcile content, don't overwrite.
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## Tidy after a cancelled sibling
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A killed subagent can leave a worktree plus an empty branch. Removing them is
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safe only when verified empty: `git -C <main> log --oneline -3 <branch>` (no
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unique commits) and `git -C <wt> status --short` (clean), then
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`git worktree remove <wt>` + `git branch -D <branch>`. An orphan worktree at a
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stale commit is the same class of trap as a leftover bench drop-in: the next
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agent reads it as unfinished work.
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## Report it
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File the misresolution to `xd://report_issue` (false positives are fine) and
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record the incident in the repo worklog — a repair nobody wrote down looks like
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a hijack later.
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