docs: design conflict-free results sync without force push

[christso]

Summary

Design artifact (docs-only) for a no-force-push results-sync workflow for AgentV Dashboard/API. Evaluates the operator's timestamped-branch + merge + delete-to-resync idea, hardens it, and recommends a hybrid:

• Auto-merge the common case. Result writes are append-mostly and line-orthogonal (immutable run bundles under runs/<exp>/<ts>/, append-only index JSONL). Replace the backup_and_force_push escape hatch with a bounded fetch → merge → push loop using artifact-aware merge drivers (merge=union for index, a JSON set/field-union driver for the small mutable overlay). A non-fast-forward becomes a real merge commit — no force push.
• Human-in-the-loop fallback only on true conflict. Push local work to a new sync-<ts>-<rand6> branch (never canonical), surface a compare/PR link, and resume canonical sync only when the contributed run bundles actually reach canonical (tree-equality / ancestor check, squash-safe) — not on branch deletion (which is unreliable and risks silent data loss).

Doc: docs/plans/2026-06-24-001-feat-conflict-free-results-sync-plan.md.

Key points

• No force push / no shared-history rewrite anywhere.
• Critiques branch-deletion-as-merge-signal; proposes robust merged-detection.
• Per-artifact-family merge strategy; concurrency handling; polling-vs-webhook (local-git, zero-infra; optional gh enrichment).
• Alternatives compared: always-PR, rebase/replay, append-only/CRDT overlay.
• Phased non-breaking plan + explicit non-goals.
• Reuses the prior metadata-conflict UX design (PR docs: design remote metadata conflict resolution #1491 / av-xwm) minus its force_push_local action.

Tracker

• Epic av-raf with phase children av-raf.1–4; related to av-xwm.

Notes

Design only; no implementation. No screenshots committed (would go to agentv-private). Relative paths in the doc are inline code, not markdown links, so the lychee link check is unaffected.

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[christso]

Updated the design to be much simpler:

• Resume is an explicit user OK button, not auto-detection. Dropped all squash-safe tree-equality/ancestor machinery.
• GitHub's PR is the conflict-resolution surface — AgentV builds no merge/diff/accept-incoming UI. Dropped the dependency on the av-xwm per-file conflict editor.
• Layer 1 still auto-merges the append-only common case via git union/JSON-union drivers (silent, no UI).
• Layer 2 (true conflict only): push a timestamped temp branch → surface a GitHub compare/PR link → user merges on GitHub → clicks OK → AgentV pulls the target branch and resumes. A premature OK just re-diverges with no data loss and no force push.

Still docs-only; tracked by epic av-raf.