Board: integrate head-bound evidence and qualify local and hosted session visibility

[jeffhuber]

Part of #945 and roadmap #900.

Problem

The presentation and session/event tracks need integrated evidence that Board tells the truth across PR, review, CI, gate, worktree, restart, freshness, and provider boundaries before it can gate Slack's end-to-end canary.

Scope

Integrate the work-first Board and automatic observation connections. Add exact-head PR/review/CI/gate evidence composition, deterministic next-actor precedence, multi-worktree/restart/stale-source regression, session outcome coverage, and a sanitized qualification scorecard. Run one real maintained local execution path and one bounded hosted Devin observation from assignment through completion/failure evidence. Test desktop and phone behavior against live-shaped, privacy-safe fixtures.

This issue validates the local Board contract only. It does not add Slack mapping, cloud fields, hosted ingest acceptance, provider mutation controls, or broad productivity claims.

Dependencies

• Board: implement the work-first Now, Timeline, Releases, and Health views #948 — work-first presentation.
• Board: connect provider-neutral remote lifecycle observations #950 — provider-neutral remote lifecycle observation connection.
• Sessions: discover the current local brief and lease from a checkout #935 discovery must be merged and exercised.

Acceptance criteria

• Active work, meaningful next action/actor, and per-source freshness are discoverable within ten seconds at desktop and phone widths.
• A fresh run without a PR is visible; review requested versus running versus changes requested is distinct; implementation completion does not imply review/merge completion.
• Behind-main plus review-needed appears once with grouped reasons and routine remediation does not inflate owner decisions.
• Gate publisher, authoritative gate verdict, required/sampled CI, exact-head audit, GitHub merge state, and human policy appear as independent evidence.
• Fresh, stale, unreachable, restarted, waiting, failed, cancelled, unlinked, no-work, multiple-worktree, and historical-running cases pass deterministic regression.
• One maintained local canary and one hosted Devin canary produce the same closed Board projection. Paid work requires explicit apply and a bounded ACU cap; uncertain create is reconciled, never blindly retried.
• Measured time/cost/outcomes include coverage; absent or partial data cannot become zero or a productivity claim.
• Privacy scans and snapshot assertions prove no private session/provider/context/Slack/Graphify/source/path content.
• The resulting Board readiness is sufficient for Release: qualify and publish Slack session ingress in v1.5.0 #923's Slack end-to-end canary/final acceptance; Slack: metadata-only Board and CodeMower.com lifecycle telemetry #921 still owns Slack/cloud mappings.

Initial ownership

Convergence issue. The roadmap orchestrator assigns one Code Mower builder after the presentation and session/event heads merge, preserving a single writer. The builder must be independent of the exact-head reviewer.

Code Mower delivery

Produce one independently reviewable PR for this issue. Record the named Code Mower builder, keep one writer on the branch, obtain an independent audit against the exact current head, resolve every P0/P1/P2 finding, and pass focused tests, full relevant regression, privacy checks, normal CI, and code-mower/gate. Upload only allowlisted metadata. No umbrella PR.