Amend asymmetric-ownership-stack doctrine with cross-agent-handoff as fourth terminal state

From 2026-06-16 self-reflection. Atomic HEARTBEAT.md (or LEARNINGS doctrine seed location) edit. Workspace-internal (no PR). The asymmetric-ownership-stack doctrine currently codifies three terminal states for a non-Cato-authored PR carrying significant Cato fix-effort with no owner engagement past ~7 days: (a) ping owner directly (b) close as abandoned with comment preserving the diff in the branch (c) hand back / leave open as placeholder ADD a fourth terminal state: (d) cross-agent handoff: if during the 7-day surface-to-Slava mute window the PR receives a fix-push from a non-Cato fleet agent (recognized by git log -1 --format='%an <%ae>' on the latest upstream commit not matching Cato's texture-coding-agent dispatch identity, or via the Co-authored-by trailer naming a different stakeholder), treat that as Slava's implicit answer: the PR continues with different ownership. Update .blockers.env with the cross-agent observation (LAST_OBSERVED_AT and NOTES), extend the mute to +14d from the cross-agent push date, and exit the surface-to-Slava recipe without a re-DM. Do not invest further Cato fix-effort unless explicitly requested by Slava. CASE STUDY (2026-06-15): PR #11790 (Winston brush-zoom-auto-densify, BOLT-1193) had 7 Cato fix-pushes across Cursor Bugbot rounds 1-7 (06-08 to 06-10). Cato surface-to-Slava DM 06-13T05:39Z with three-option ask (a/b/c). Slava silent across 06-13/06-14/06-15. At 06-15T16:25:36Z, texture-coding-agent (Richie's agent or shared fleet agent acting on Richie Casto's V-notch repro) pushed c201fb07 — clean semantic commit threading a curve prop through AreaSeries + d3-shape re-exports + 3 new tests + 1783/1783 edges, 49/49 SiteEnergyCharts. No collision with Cato's prior commits; co-author trailers preserved; branch ahead by exactly one well-formed commit. Slava implicitly chose path (d) over (a/b/c). ATOMIC STEPS: 1. Locate the asymmetric-ownership-stack doctrine in HEARTBEAT.md (or wherever it lives currently — may be in the muted-PR escalation section). 2. Add the fourth terminal state with the case study. 3. Verify edit clean. 4. PATCH this task to completed via bin/fleet-task-patch.sh with file:line of the amendment.