skills/ce-babysit-pr/references/branch-currency.md

# Branch currency (third stream)

Consume only the exact `branch_currency` item the snapshot emitted. No item means no base-into-head mutation, whatever else moved.

6. **Branch currency & conflicts (the third stream — after comments and CI).** Consume the exact current `branch_currency` item; never infer a new item from merge-state prose. `UNKNOWN` mergeability or any non-null `base_ref_blocker` yields no item and is only re-polled. Managed stacks and `probe-error` are excluded from this route. A `normal-base` item may be target-local for an independent PR or an eligible manual dependency; do not redirect a manual dependency to its parent. An open child dependent does not disqualify a root PR, but this route never rewrites, rebases, or mutates dependent heads.
   - **Inspection and claim lifecycle.** Source evidence retains ordinary mutation-safety facts when a grouped decision is invalidated. If `attention == "decide"`, return the exact currency source through the shared typed-residual boundary and do not claim it; only an exact matching recorded answer can authorize another mutation. If `attention == "inspect"`, first preview the current conflict and compute its semantic conflict fingerprint. Compare it with `parked_semantic_fingerprints`, then mark the exact item with `--currency-inspected-fingerprint <fingerprint>`. Unchanged evidence stays parked; changed evidence retires the old park and reopens the item. Do not claim before that inspection clears. For `attention == "claim"`, and only while fixed budget remains, atomically mark the exact item **before any external mutation or local merge starts**:

     ```bash
     SKILL_DIR="<absolute path of this skill's directory>"; STATE_DIR="<the $STATE_DIR resolved above: $SCRATCH_ROOT/ce-babysit-pr/<host>-<owner>-<repo>-<N>>"; RUN_INVOCATION_ID="<invocation_id>"; RUN_STARTED_AT="<invocation_started_at>"; RUN_BUDGET_SECONDS="<invocation_budget_seconds>";
     PY="$(for c in python3 python py; do command -v "$c" >/dev/null 2>&1 && "$c" -c '' >/dev/null 2>&1 && { echo "$c"; break; }; done)"; [ -n "$PY" ] || { echo "no working Python 3 interpreter on PATH" >&2; exit 1; };
     "$PY" "$SKILL_DIR/scripts/pr-snapshot" mark --state-dir "$STATE_DIR" --invocation-id "$RUN_INVOCATION_ID" --session-started-at "$RUN_STARTED_AT" --invocation-budget-seconds "$RUN_BUDGET_SECONDS" --currency-key <currency_key> --currency-disposition claimed
     ```

     A re-entry into `claimed` is reconciliation-only: inspect remote and local evidence, never directly resubmit. Record exactly one of `--currency-outcome mutation-observed`, `--currency-outcome proven-no-mutation`, or `--currency-outcome ambiguous`. Continue autonomously only through the recovery the recorded outcome leaves safe: reconcile an observed mutation toward confirmation. Exactly one retry is possible only after conclusive no-mutation proof and the engine's backoff. An ambiguous result never retries or resubmits. Confirm against the same `--currency-key`. Every terminal currency result with no safe autonomous continuation owns one complete typed residual with source `{ id: <currency_key>, kind: "currency" }` in that same locked command through `--residual-file`. This creates the same decision record used by review and CI; currency has no separate parked or answered decision state. Consume a human answer through the shared `--answer-decision <decision_id> --answer-file <path>` transition in `tick.md`, then act on the reactivated exact observation. A stale invocation, exhausted budget/`max-runtime`, or head/base movement between claim and mutation rejects or invalidates the action before it writes.
   - **`BEHIND`: host-owned update only.** Proceed only for `route == "normal-base"` with `host_branch_update_capability == true`; `false`/denied or `unknown` is a `needs-human` path, never inferred from Git or direct-push authority. After claim, immediately revalidate that remote head and base OIDs still equal the observation. Invoke the host update operation once through GitHub's `PUT /repos/{owner}/{repo}/pulls/{number}/update-branch` endpoint with `expected_head_sha` set to the claimed observation's head SHA; never use an update helper that cannot transmit that precondition. Treat an HTTP 422 head mismatch as a stale claim: re-snapshot and reconcile without resubmitting. Host acceptance is `mutation-observed`, not completion. Confirm the exact claimed observation only after a fresh snapshot and ancestry evidence prove the resulting head contains its observed base OID and no unrelated head/base movement or different current currency evidence invalidates that proof. The claimed item's own `branch_currency_blocker` remains until confirmation and need not be null beforehand. A moved head alone is not proof.
   - **`DIRTY`: exact-base local repair only.** `host_branch_update_capability` is irrelevant and does not imply push access. Separately prove, without mutating, ordinary direct-push authority to the exact head ref; unknown or denied authority requires the shared typed decision above. Require a verified clean PR-head checkout at the observed head, fetch the exact observed base OID, and run a non-mutating merge preview. The semantic conflict fingerprint is the sorted conflicted paths plus their stage blob identities; it excludes the base OID so unrelated later base movement cannot disguise the same conflict. A resolution is mechanical only with **positive intent evidence** and **no reasonable alternative behavior**. Two plausible resolutions, a material behavior or user-intent choice, unbounded scope, stale OIDs, incomplete evidence, or missing authority means abort safely and pass `--semantic-conflict-fingerprint <fingerprint>` with the shared residual mark, concrete options, tradeoffs, and a lean.
   - **Apply and confirm a mechanical `DIRTY` repair.** Claim and revalidate the exact head/base OIDs and clean checkout again, merge that exact base OID, and mark `--currency-outcome mutation-observed` as soon as the local merge starts. Resolve only the previewed mechanical conflict, validate proportionally, and use a normal push to the exact head ref. Never rebase or force-push. An interrupted local merge must be reconciled to its validated commit or aborted safely before parking; never layer a second attempt over it. Confirm only when remote evidence proves the head equals or contains the validated merge commit, a fresh snapshot clears the currency gate, and no unrelated movement invalidated the claim. **Remote head movement alone is not proof or confirmation.**
   - **Managed stack or probe uncertainty.** With `manager_status == "confirmed"`, manager currency outranks ordinary state: pre-existing target staleness becomes `stack-sync-needed`, never this route; Step 7 alone owns post-push manager maintenance. With a manager or relationship `probe-error`, continue review/CI but perform no branch-currency mutation or ready declaration until classification succeeds.

## `unrequested_base_merge` (defect detector)

The snapshot flags a head that is a two-parent merge of the base tip when no claimed currency item produced it (`unrequested_base_merge: {head, base_parent}`; wake reason `unrequested-base-merge`). That is the incident shape — main moved, someone merged it into a CLEAN PR, green CI restarted — not maintenance. Report it in the tick summary as a defect residual, name who pushed it if the commit tells you, and keep watching; never undo it with a rebase or force-push, and never treat the resulting `BLOCKED`-while-checks-rerun as a new blocker. It clears itself on the next head.