docs(contributing): add self-collision preflight draft for intra-lane duplicate PRs

[sramkrishna]

bluefin-common PR

What does this change?

Adds docs/contributing/self-collision-preflight.md — a planning draft for a
preflight step that intersects a lane's own open PRs before it files again — and
links it from CONTRIBUTING.md, docs/factory/agentic-model.md, and
docs/skills/pr-review/references/duplicate-cluster.md.

Why?

Closes #1060

The hold-gated protocol lists open PRs at kick time precisely so a lane can prove
its new filing is disjoint from work already in flight. Within one lane that
check failed: the quality lane opened two duplicate pairs covering identical file
clusters within three days (finpilot#285/#303, finpilot#296/#299), costing
four review slots for two pieces of work.

All four named PRs are already resolved — #285 merged 2026-09-04, #296
merged 2026-09-05, #299 merged 2026-09-06, #303 closed 2026-09-06 without
merge. The queue adjudicated them rather than any rule preventing the second
filing, so the actionable remainder is the rule.

Why this is a draft and not a direct edit to the hard rules

The issue proposes "a lane may not open a PR whose file cluster intersects its own
open hold-gated PRs." I re-audited the 31 open app-authored PRs across the ten
repositories tracked in #1058 on 2026-09-23 and found no confirmed intra-lane
duplicate cluster. Every file-cluster intersection that exists is legitimate
work the prohibition would have blocked:

Intersecting pair	Same lane?	Why it is not a duplicate
bluefin#1227 / #1310	app/mergeraptor	Distinct dependency digest bumps (projectbluefin/common:latest vs ublue-os/brew:latest) sharing image-versions.yml
server#238 / #239	app/mergeraptor	Distinct dependency digest bumps (projectbluefin/actions vs taiki-e/install-action) sharing .github/workflows/build.yml
dakota-iso#142 / #146	app/hivecommons-hive	A cosign-verification security fix and a host-side config SSOT refactor, both touching justfile
common#1186 / #1187	human (repires)	Two human PRs closing different issues (#1161, #1160) sharing Justfile and .github/workflows/unit-tests.yml

A shared file is not proof of duplication — that is already the factory's rule at
review time (common-rationalizations.md,
duplicate-cluster.md).
The real finpilot duplicates shared an intent and closing issue, not merely a
path. So the draft proposes the evidenced alternative: intersect, compare hunks
and closing-issue sets, then either comment on the existing PR or disclose the
overlap in the new body — a disclosure rule rather than a prohibition, which
keeps the judgment where the evidence is and makes it visible to the reviewer.

It is drafted rather than applied because it binds filing behavior org-wide. That
matches the precedent set for the sibling strategist findings: #1043 →
hold-gate-rubric.md (#1188) and #1052 → agent-lane-throttle.md (#1197), both
merged as drafts pending a maintainer decision. Nothing in the draft changes agent
runtime behavior, adds a label, or adds a CI gate.

PR pipeline

opened ──▶ 4-review ──▶ approved ──▶ merged

A maintainer reviews and approves; merge goes through the merge queue.
Select blocked or hold to pause the work.

Checklist

• PR title follows Conventional Commits (fix:, feat:, docs:, ci:, refactor:, etc.)
• just check passes
• pre-commit run --all-files passes (all 15 hooks green, including skill front-matter, docs/SKILL.md index, internal markdown links, and the generated docs/skills/index.json catalog)
• Skill doc updated if the change affects agent-facing conventions or behavior — docs/skills/pr-review/references/duplicate-cluster.md gained a prevention pointer to the draft; docs/factory/agentic-model.md gained a pointer from the existing duplicate-PR rule
• AGENTS.md / docs/SKILL.md / docs/skills/ links remain valid (scripts/check-doc-links.sh passes)
• CI is green after push — pending

AI attribution

This change was not authored via GitHub Copilot, so the Copilot-specific
Co-authored-by trailer is deliberately omitted rather than asserted. The
attribution trailer names the actual model:

Assisted-by: deepseek/deepseek-v4.1-flash via Hive

— hive: backend=litellm model=deepseek/deepseek-v4.1-flash

🐝 Hive Agent: contributor | SHA: a8fcea8

[castrojo]

LGTM. Clear, evidenced planning draft for intra-lane duplicate PR preflight checks without adding CI overhead.

[Danathar]

This PR adds a draft proposal, docs/contributing/self-collision-preflight.md, and links to it from CONTRIBUTING.md, agentic-model.md and duplicate-cluster.md. I read the whole diff at a8fcea8. I checked the finpilot PR dates, outcomes and file clusters, the four intersecting pairs, the linked issues, and the internal links and anchors, and they all hold up. The gh pr list … --json number,title,files command also works as written. Locally, just check, tests/test_skill_docs.py, generate_skill_index.py --check and check-doc-links.sh all passed. Validate PR run 35929017936 is green, and Build is path-ignored for docs.

One sentence is wrong. The line added to agentic-model.md says "The topic search does not cover the lane's own open PRs". But gh pr list --state open --search "<topic>" has no author filter, so it does return the lane's own PRs. The real gap is that it matches on text, not on changed files.
Evidence: finpilot#296 and #299 both have "tag-images" in the title, so a topic search for it would have returned both.
Maybe something like: "The topic search matches on text, not on changed files, so it can miss the lane's own open PRs that touch the same files under a different title."

[hanthor]

This is a planning doc only, so it's fine to land as a draft proposal. Heads up: it will conflict trivially with #1189 in CONTRIBUTING.md, whichever one lands second.