refactor(mqlaunch): make mq-ui.sh the single print_header authority (Step 11a)

[MCamner]

What

Resolve the print_header duplication the git de-layer surfaced (#45). The launcher redefined print_header after sourcing mq-ui.sh, shadowing the library's version.

The two were not cosmetic variants: the launcher override re-forked the dashboard script uncached on every screen, bypassing the dashboard cache model (TTL + mq_dashboard_cache_invalidate) that the rest of the runtime — the git/release flows, the cache smoke test — already relied on. The override was the anomaly that ignored its own caching infrastructure.

• Remove the launcher override → mq-ui.sh is the sole print_header owner.
• Opt the main loop into the dashboard-v7.1 header via a non-exported MQ_USE_DASHBOARD_HEADER=1 (non-exported so it drives this launcher's print_header without forcing the dashboard header onto child subprocesses, which set the flag themselves).
• Delete the now-dead DASHBOARD_V71 variable (only the removed override used it).

Launcher: 1348 → 1347 lines (the override's logic collapses into the single-line opt-in).

Behavior change (deliberate — chosen with the maintainer)

The main-loop header now renders through mq-ui's cached dashboard path instead of an uncached per-screen fork:

• Freshness bounded by MQ_DASHBOARD_CACHE_TTL (default 5s), invalidated by open_git_menu / open_release_menu so a commit/stash/tag refreshes immediately.
• Removes a hidden fork in render behavior; aligns the main loop with the cache + invalidation model the runtime already used; avoids a dashboard re-fork per screen.
• Escape hatch: MQ_DASHBOARD_CACHE_TTL=0 restores uncached, per-screen rendering for investigation.

Verification

• Confirmed the dashboard header still renders in the main loop under launcher conditions; the cached path populates and reuses within TTL (no fork per screen).
• Full selftest suite green — including the dashboard-header-cache contract (rapid renders reuse cache; invalidation forces refresh; TTL=0 disables) and headless smoke.
• AUTHORITY_MAP updated: mq-ui.sh marked sole print_header owner.

Completes the print_header thread flagged in #45/#47. Part of the v2.0.0 runtime-authority track.

🤖 Generated with Claude Code

[MCamner]

Decision note (of record)

This change intentionally unifies print_header behavior around the mq-ui.sh implementation.

Before this change, the launcher-level print_header override did more than change presentation. It re-ran the dashboard script uncached on every screen, which bypassed the existing dashboard cache model. In contrast, mq-ui.sh renders the cached dashboard when MQ_USE_DASHBOARD_HEADER=1, with a 5-second TTL and explicit invalidation hooks already used by the git/release flows.

That made the launcher override a behavioral anomaly: the repo had cache infrastructure, invalidation calls, and cache smoke coverage, but the main loop was still using an uncached path.

This PR standardizes the main-loop header on the cached mq-ui.sh path. The intended result is one header contract, one freshness model, and one cache/invalidation mechanism across the runtime.

Behavior change

• main-loop header rendering now uses the cached dashboard path by default
• header freshness may be up to 5 seconds old unless the cache is explicitly invalidated
• existing invalidation hooks (open_git_menu / open_release_menu) now apply consistently to the main-loop header

Why this is the preferred behavior

• removes a hidden fork in render behavior
• aligns runtime behavior with the repo's existing cache design
• makes cache invalidation meaningful and consistent
• reduces repeated dashboard re-forks on every screen render

This is a deliberate behavior decision, not a cosmetic cleanup.

Risk

• any workflow that implicitly depended on per-screen uncached freshness will now see cached header behavior instead

Escape hatch (correction to the original draft)

MQ_DASHBOARD_CACHE_TTL=0 is a pre-existing, permanent cache bypass (already covered by tests/dashboard-header-cache-smoke.sh), not a temporary mitigation added by this PR. It remains available indefinitely as the uncached / force-fresh switch for investigation or debugging.

Follow-up

• validate the cached path in normal use
• no escape hatch removal is needed — MQ_DASHBOARD_CACHE_TTL=0 stays as the permanent uncached switch

🤖 Recorded via Claude Code