Start / resume a topic chat — orient before you touch anything

The opening bookend of the session lifecycle (the mirror of /handoff, the closing one). If you run several topics in parallel — each on its own branch, often its own git worktree — a fresh chat has zero context and the #1 failure mode is working in the wrong folder/branch or on top of another chat's half-finished edits. This skill removes that: it lands you on the right branch, confirms the tree is clean (or surfaces exactly what's dirty and why), syncs with origin, and hands you the resume summary from the latest handoff doc.

/start is orient-FIRST. It may git fetch and fast-forward pull, and it READS docs — but it never commits, never pushes, never discards another chat's work. The one write it may do is gated: if the topic has no branch/worktree yet, offer to create one — shown in full, run only on an explicit yes.

Step 1 — Resolve the branch / worktree

Figure out where this topic lives:

git worktree list          # if you use one worktree per topic
git branch --list          # otherwise, the topic's branch

• Topic maps to a worktree → that folder is where you work; all later git ops use git -C <worktree> … and edits use absolute paths under it.
• Topic maps to just a branch → git switch <branch> (only if the current tree is clean; if dirty, STOP and report — don't switch over uncommitted work).
• No topic given → list the worktrees/branches and ask which one; don't guess.
• No branch/worktree yet (new topic) → offer to create it (gated — show the command, run on yes):

  # branch only:
  git switch -c <topic>
  # or a dedicated worktree off your integration branch:
  git worktree add -b <topic> ../<topic> <base-branch>

Step 2 — Clean-tree check (the contamination gate — the point of this skill)

git -C <worktree> status --porcelain

Classify — do not auto-clean anything:

• Empty → clean. Say so and continue.
• Dirty with THIS topic's files → likely legit in-progress work the last handoff mentions. Cross-check against the handoff (Step 4); if it lists these as "uncommitted", report as resume-in-progress and leave it.
• Dirty with files that don't fit this topic → contamination flag. Surface the exact files, say they look out of place, and ask whether to leave, move, or (only on explicit say-so) discard. NEVER git stash/reset/checkout/clean without an explicit instruction — another chat may own that work.

Step 3 — Sync with origin (safe, fast-forward only)

git -C <worktree> fetch origin
git -C <worktree> status -sb        # read ahead/behind vs origin/<branch>

• No upstream (fresh branch) → report it and skip the pull (a bare pull --ff-only errors "no tracking information"). /commitpush will set the upstream when you first push.
• Behind & clean → git -C <worktree> pull --ff-only. Report the new tip.
• Behind & dirty → do NOT pull (could conflict); report "behind by N, pull after committing."
• Ahead → note "N local commits not pushed" (normal).
• Diverged → report it; don't auto-merge/rebase — let the user decide.

Step 4 — Load the resume context (handoff → destination doc)

Find the newest handoff doc for this topic (see the /handoff skill — default folder handoffs/, overridable with HANDOFF_DIR):

HO="${HANDOFF_DIR:-$(git rev-parse --show-toplevel)/handoffs}"
ls -t "$HO" | grep -iE '<topic>'      # newest first

• Read the newest match; confirm its title/DESTINATION DOC line names the expected topic before trusting it (guards against a newest-but-mismatched file). Follow its DESTINATION pointer and read that doc too.
• No handoff found? Say so and fall back to the topic's README/plan + recent git log.
• Treat a handoff as a map: read the docs it names (and the docs THOSE name) before claiming the picture is loaded.

Step 5 — Report the orientation (concise, actionable)

• Folder + branch: "Working in <worktree> on <branch>."
• Tree state: clean ✅ / resume-in-progress (list files) / ⚠️ looks-contaminated (list + what you asked).
• Sync: ahead/behind vs origin; whether you fast-forwarded.
• Where we are / what's left: 3–6 bullets from the handoff + destination doc — current state, what's done, and the next concrete task(s).

Then stop and let the user direct the work. Do not start editing as part of /start — orientation only.

Don'ts

• Don't work in the wrong folder, and don't edit two topics from one chat.
• Don't stash/reset/checkout/clean/-A anything as part of orientation — surface it and ask.
• Don't pull when dirty; don't auto-merge/rebase a divergence.
• Don't commit, push, or change code — /start is read + fast-forward only (plus the one gated create-worktree offer).