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+---
+pr_number: 3873
+title: "shard(tick): 2026-05-16T12:36Z \u2014 pure-git tier; 2nd multi-Otto contamination in 3 ticks"
+author: "AceHack"
+state: "MERGED"
+created_at: "2026-05-16T13:01:49Z"
+merged_at: "2026-05-16T13:03:20Z"
+closed_at: "2026-05-16T13:03:20Z"
+head_ref: "otto-cli-tick-2026-05-16-1236z"
+base_ref: "main"
+archived_at: "2026-05-16T13:08:34Z"
+archive_tool: "tools/pr-preservation/archive-pr.ts"
+---
+
+# PR #3873: shard(tick): 2026-05-16T12:36Z — pure-git tier; 2nd multi-Otto contamination in 3 ticks
+
+## PR description
+
+Deferred-PR landing under pure-git tier discipline (branch pushed when GraphQL=0).
+
+## Shard
+
+[`docs/hygiene-history/ticks/2026/05/16/1236Z.md`](docs/hygiene-history/ticks/2026/05/16/1236Z.md) — 2nd multi-Otto contamination observation of this session. HEAD bounced back to the PR #3871 branch under peer-Otto's `fix_branch` shell function (PID 75933 observed at 12:21Z firing `git switch <branch>` against the shared `.git/`).
+
+## Pattern stable
+
+| Tick | HEAD at tick start |
+|---|---|
+| 12:11Z | `otto-cli-b0206-audit-2026-05-16-1207z` (own) |
+| 12:21Z | `otto-cli-b0037.2-audit-2026-05-16-1131z` (peer MD018 branch) |
+| 12:36Z | `otto-cli-b0206-audit-2026-05-16-1207z` (bounced back) |
+
+Defense pattern (`git branch --show-current` + `git switch -c <fresh> origin/main`) 100% effective. B-0519 RCA confirmed at high cadence.
+
+## Reviews
+
+### COMMENTED — @copilot-pull-request-reviewer (2026-05-16T13:03:09Z)
+
+## Pull request overview
+
+Adds a hygiene-history tick shard recording the 2026-05-16T12:36Z autonomous-loop observation and the pure-git operating tier under GraphQL exhaustion.
+
+**Changes:**
+- Documents the second multi-Otto HEAD-contamination observation in three ticks.
+- Records the pure-git tier decision, deferred PR backlog, sentinel status, and visibility signals.
+- Links the branch-push counter rationale to the existing refresh-world-model poll PR gate rule.