Changes touching this path

• Fix #128: pull/apply collapses a concurrent two-writer fork (#129) Engine `apply_sync` ingests a peer's divergent tip as a *sibling head* and classifies per-path outcomes, but never merges tips — so a keyholder that had also advanced its own line was left on two heads with a working tree showing only its own side (the peer's content in the graph but never materialized). No CLI verb converged it (`dock merge` is docks-only). This is the gap the concurrent-agents proof surfaced under a real run. Add `Workspace::converge_heads(base)` — the peer-side analogue of `merge_dock` (ADR 0011: keyholders collapse forks on pull+apply). It folds every other head into our line via `merge_tips`, signs each merge so it travels, then materializes the merged tree (visibility-aware: a sealed path the identity can't open stays relayed, not dropped). `cmd_pull` calls it after the batch loop, passing the pre-pull head as our side, and now also honors `--porcelain`/`--json` like the other reconciliation verbs. Proven end to end by docs/evidence/scripts/concurrent-agents-demo.ps1 — both acts pass: Act 1 (local docks → harbor, real conflict + resolve + buoy), Act 2 (two identities push concurrently, relay DAG forks, agent's pull collapses it; public converges with no side dropped, restricted path relays R). Regression test: converge_heads_collapses_a_two_writer_fork_no_side_dropped. Git-Author: Connor Miller <53197564+Connor-Miller@users.noreply.github.com> bb4c849f

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