diff --git a/docs/backlog/P3/B-0174-cross-model-tool-review-convergence-rate-replay-otto-2026-05-03.md b/docs/backlog/P3/B-0174-cross-model-tool-review-convergence-rate-replay-otto-2026-05-03.md
new file mode 100644
index 000000000..21ae4109c
--- /dev/null
+++ b/docs/backlog/P3/B-0174-cross-model-tool-review-convergence-rate-replay-otto-2026-05-03.md
@@ -0,0 +1,85 @@
+---
+id: B-0174
+priority: P3
+status: open
+title: Cross-model tool-review convergence-rate replay protocol — measure how many review rounds different models need to settle on a tool-authoring PR (Otto 2026-05-03 sibling-instance of multi-harness convergence skill domain)
+tier: research
+effort: M
+ask: Otto self-derived 2026-05-03 from v0.5 substrate-claim-checker review-cycle empirics + Aaron 2026-05-03 nudge to formalize as backlog row (autonomous-loop maintainer channel)
+created: 2026-05-03
+last_updated: 2026-05-03
+depends_on: [B-0170]
+composes_with: [B-0169, B-0173]
+tags: [calibration, multi-harness, cross-model, frontier-ability, convergence, code-review, tool-authoring, p3-research]
+---
+
+# Cross-model tool-review convergence-rate replay protocol
+
+## Origin
+
+Otto 2026-05-03, observing the v0.5 substrate-claim-checker review-cycle (PR #1298) accumulate 19+ substantive findings across 5 rounds with a clear convergence trend (8→5→2→2→2 stabilizing at 2/round). Per Aaron 2026-05-03 nudge to formalize as backlog row rather than leave as a memo observation.
+
+This is a **sibling-instance** of the multi-harness alignment convergence future-skill-domain memo (`memory/feedback_multi_harness_alignment_convergence_design_future_skill_domain_aaron_2026_05_03.md`). The parent memo covered design-time convergence (run designs through N harnesses × M models). This row covers iteration-time convergence (how many review rounds does a model need to settle on a tool-authoring PR).
+
+## What it measures
+
+For a given AI model M and a tool-authoring task T:
+
+1. Give M the initial draft of T (e.g., v0.5 substrate-claim-checker check-existence.ts)
+2. Run a fixed code-review prompt against the draft (using Otto's own reviewer-style or a standard reviewer harness)
+3. M produces a revised draft addressing the findings
+4. Run code-review prompt again
+5. Repeat until 0 findings (convergence) or N rounds (timeout)
+6. Record: per-round-finding-count, total-rounds-to-converge, total-findings, finding-categories-per-round, code-quality-delta (LOC, test coverage, etc.)
+
+The **convergence-rate signature** is `[findings_round_1, findings_round_2, ..., 0]` — a per-model fingerprint of code-authoring quality.
+
+## Comparison points
+
+- **Otto baseline (this session)**: v0.5 check-existence.ts: 8→5→2→2→2 (5 rounds and counting; not yet converged). Categories: security, cross-platform, false-positive scope, regex edge cases, test discipline + extension whitelist
+- **Other models**: GPT-5.x (Codex), Claude.ai (different harness), Gemini, Cursor's models. Each gets the same initial draft + same review-prompt; observe their convergence-rate
+
+## Why this is research-grade calibration data
+
+- **Reproducible** — same tool draft + same review prompt = directly comparable across models
+- **Quantitative** — finding-counts are measurable; convergence-rounds are measurable
+- **Frontier-ability signal** — models with faster convergence-rate produce higher-quality code per cycle
+- **Composes with the calibration protocol** — Otto's in-the-moment guesses (B-0XXXX backlog rows) measure architectural-intent inference; this row measures code-implementation quality
+
+## Acceptance criteria
+
+This row closes when:
+
+1. Protocol is documented (per-step, with example fixtures): how to feed a tool-draft to a model, how to run the review-prompt, how to record the finding stream, how to detect convergence
+2. At least 3 cross-model runs are executed against a fixture tool-draft (e.g., the v0.5 initial check-existence.ts)
+3. Results are published in `docs/research/cross-model-convergence-rate-replay/` with the per-model convergence signature + categorical breakdown
+4. The protocol is referenced from the multi-harness convergence skill-domain memo as a worked-example seed
+
+## Composes with
+
+- **B-0170** (substrate-claim-checker tool) — depends_on; the v0.5 review-cycle is the empirical seed
+- **B-0169** (decision-archaeology skill) — composes_with; Otto's convergence-signature is part of decision-archaeology data for "how this tool came to be"
+- **B-0173** (hook authoring) — composes_with; hooks could automate the review-prompt invocation
+- `memory/feedback_multi_harness_alignment_convergence_design_future_skill_domain_aaron_2026_05_03.md` — parent skill domain
+- `memory/feedback_guess_then_verify_architectural_intent_calibration_protocol_aaron_2026_05_03.md` — sibling protocol (architectural-intent inference vs code-implementation quality)
+- `memory/architectural-intent-guesses/` — sibling calibration data directory
+
+## Why P3
+
+This is research-grade frontier-ability measurement, not a production-blocking concern. P3 (low-priority research) per the project priority taxonomy. Promotion to P2 would be appropriate when:
+
+- 3+ cross-model runs are scheduled to run as a routine (not one-shot)
+- The convergence-signature data starts informing model-selection decisions for routine work
+- Aaron names it as a recurring need rather than a research curiosity
+
+## Effort sizing — M (medium)
+
+- Designing the review-prompt + fixtures: small
+- Running first cross-model batch: medium (depends on harness availability + per-model latency)
+- Documenting the protocol + writing the per-model results: small-to-medium
+
+Total: M. Bounded; not multi-month. Mostly composing existing infrastructure (harnesses + review-prompt + tool fixtures).
+
+## Carved sentence
+
+**"Cross-model tool-review convergence-rate replay measures how many review rounds different AI models need to settle on a tool-authoring PR. Sibling-instance of the multi-harness alignment convergence future-skill-domain. Otto's v0.5 substrate-claim-checker review-cycle (8→5→2→2→2 stabilizing at 2/round) is the empirical seed. Reproducible, quantitative, frontier-ability-revealing. Closes when protocol is documented, 3+ cross-model runs executed against a fixture, results published in docs/research/cross-model-convergence-rate-replay/."**