docs: correct merge strategy to squash-only in collab spec

[JasonJarvan]

Summary

The AI-collaboration spec (AGENTS.md, which CLAUDE.md symlinks to) claimed the repo uses rebase merge (not squash) and, from that, that every commit's body/trailer lands on main verbatim. GitHub is actually configured squash-only: allow_squash_merge=true, allow_rebase_merge=false, allow_merge_commit=false. Under squash-merge a PR collapses to a single commit on main, so per-commit trailers are lost — the exact opposite of what the spec assumed.

This doc-only change corrects the merge-strategy wording so the guidance matches reality:

• 3.3 — state squash-merge (rebase / merge-commit disabled) as the integration method; the Co-authored-by trailer must live in the PR description, not only a commit body.
• 3.7 trailer rule — promote the "if the repo ever switches to squash-merge" hypothetical into a current, unconditional rule: the PR description must end with Co-authored-by: ..., else the squash commit loses the trailer.
• 3.5 / 3.6 — reframe sync-before-push: still recommended (avoids stale-base conflicts and merge-commit noise), but rebase is no longer required for a linear history since main squash-merges, and a plain git merge origin/<target> is an acceptable alternative. Noted that check_commit_messages.py now runs with --no-merges, so a merge commit on your branch won't fail lint.

No rule clauses were changed — only the merge-strategy framing.

Type

• Fix
• Feature
• Docs
• CI / tooling
• Refactor
• Other

Verification

• Reviewed GitHub merge settings: gh api repos/EverMind-AI/Raven --jq '{rebase:.allow_rebase_merge,merge:.allow_merge_commit,squash:.allow_squash_merge}' returned {"rebase":false,"merge":false,"squash":true}.

• Confirmed scripts/check_commit_messages.py runs git log --no-merges ... (introduced in ci: skip merge commits in commit-message lint #90).

• grep -niE "rebase[ -]merge|verbatim" AGENTS.md — no stale wording remains.

• Relevant tests pass locally

• Relevant lint / type checks pass locally

• User-facing docs or screenshots are updated when needed

Note: docs-only change, no code paths touched, so no unit tests apply. The pre-commit hooks (including the commit-message lint) passed on commit.

Risk

• Security impact considered
• Backward compatibility considered
• Rollback path is clear for risky changes

Related Issues

N/A

Co-authored-by: Claude (claude-opus-4-8) noreply@anthropic.com