shard(tick): 2026-05-16T12:21Z — multi-Otto contamination caught at tick start

docs/hygiene-history/ticks/2026/05/16/1221Z.md

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+# Tick 2026-05-16T12:21Z — Otto-CLI
+
+Autonomous-loop cron fire. **Multi-Otto contamination observed**
+— HEAD had moved to peer's branch
+(`otto-cli-b0037.2-audit-2026-05-16-1131z`) between this tick
+and the prior 12:11Z tick. Same-process empirical anchor for
+[B-0519](../../../../../backlog/P3/B-0519-multi-otto-branch-state-contamination-rca-2026-05-14.md).
+
+## Refresh result
+
+| Surface | State |
+|---|---|
+| Cron sentinel | `c9705646` armed (healthy across consecutive ticks) |
+| Rate limit (GraphQL) | **788/5000 — extreme cost-aware tier** (200-1000) |
+| Rate limit (core) | 4909/5000 |
+| Lior process | ACTIVE (3 processes, ongoing) |
+| HEAD at tick start | `otto-cli-b0037.2-audit-2026-05-16-1131z` (peer's branch, NOT my 12:07Z PR branch) |
+| WT state | clean |
+| Main head | `80c9b67` (11:36Z shard — audit-queue still progressing) |
+
+## Multi-Otto contamination observed
+
+Between the 12:11Z tick (which ended with HEAD on
+`otto-cli-b0206-audit-2026-05-16-1207z` after PR #3871 land)
+and this 12:21Z tick (started with HEAD on
+`otto-cli-b0037.2-audit-2026-05-16-1131z`), the primary
+worktree's HEAD silently moved. This is exactly the
+B-0519 pattern: multiple Otto-CLI processes sharing one
+physical worktree, executing `git checkout <branch>` against
+the shared `.git/`, silently moving HEAD between any two
+Bash-tool calls of THIS session.
+
+**Defense applied**: `git branch --show-current` at tick
+start caught it. Did NOT commit anything to peer's branch.
+Switched off via `git switch -c <fresh-branch> origin/main`
+to start a clean isolated tick. No `git worktree add`
+(Lior-active hazard avoided).
+
+## Operational tier picked
+
+**Extreme cost-aware** (200-1000 GraphQL remaining):
+
+- ≤1 PR-create call this tick
+- No `--all-open` batch polling
+- No `gh api graphql` thread sweeps
+- Inline `gh api rate_limit` (REST, free) verified pre-tick
+
+## Work picked
+
+Shard-only tick. The contamination observation IS the work:
+preserves the same-session empirical evidence onto a
+substrate path discoverable to future-Otto. Audit cycle
+remains 38/38; PR #3871 (12:07Z+12:11Z bundle) still in CI
+with auto-merge armed. No additional triage substrate this
+tick.
+
+## Sentinel + close
+
+`CronList`: `c9705646` armed (verified at tick start).
+
+## Visibility signal
+
+- Cron sentinel healthy
+- Multi-Otto contamination caught at tick start via
+  `git branch --show-current`; B-0519 empirical anchor
+  preserved
+- Fresh branch `otto-cli-tick-2026-05-16-1221z` from
+  `origin/main`; ls-tree canary will fire before push
+- Defense-in-depth: avoided `git worktree add` (Lior-active);
+  used `git switch -c` (no shared-pack-dir contention)
+- PR #3871 (prior tick) remains in-flight; will be acted on
+  in a future tick if it surfaces a named blocker