FM cockpit: vessel-narrow (~314px) layout — rail behavior + zone priority

Context

The ~314 CSS px vessel window (a popped-out narrow detail window; the Retina-corrected geometry from #15649's visual-matrix review) currently renders the FM cockpit clipped and unreachable-by-scroll: at a 314px viewport the cockpit measures ~971px scrollWidth against a 314px body, so the Start fleet button and right-hand content are simply off-window.

This is a layout surface, not a paint fix. Measured while working #15649:

• .fm-fleet-cockpit carries flex: 1 0 100%; with default min-width: auto its floor is the widest child's min-content (the nowrap .fm-spine-banner, ~536px).
• .fm-spine-banner has flex: none + white-space: nowrap — its ellipsis rules never engage (shrink forbidden).
• Each descendant needs its own shrink floor (grid zone wrapper, cards grid, card, stream) — zeroing them one level at a time just pushes the pressure down the tree until both dock zones collapse toward their padding boxes (fleet zone 32px, stream 28px) while the right-edge rail keeps its share.
• Conclusion: the honest fix is a vessel-narrow LAYOUT decision (rail behavior + zone priority at narrow widths), not per-element floors.

Live latest-open sweep: checked latest 20 open issues at 2026-07-21 ~20:20Z; no equivalent found. A2A in-flight claim sweep (last 60 min): no competing claim.

The Fix (design surface)

Define and implement the cockpit's vessel-narrow layout: what the right-edge rail does at ~314 (collapse to icons? hide? bottom-dock?), which zone wins the width (fleet grid vs activity stream), and how the cockpit bar wraps with the banner ellipsizing. The spine banner's flex: none shrink-forbiddance is part of the surface regardless of the chosen shape.

Acceptance Criteria

• At a 314 CSS px window the cockpit's interactive core (cards, Start fleet, pop-out toggle) is reachable — wrap, collapse, or scroll by explicit design
• .fm-spine-banner ellipsizes under pressure instead of forcing layout width
• The cockpit-vessel-314 visual receipt (FleetCockpitVisual.spec.mjs) is regenerated at the repaired layout, with the overflow assertion removed
• No regression to the desktop baselines (default shell, fleet grid, activity stream)

Related

• #15649 (tonal/breakpoint lane that surfaced this; its cockpit-vessel-314 receipt witnesses the current state), #15652 (detail-pane ~271 geometry — sibling vessel geometry)

Origin Session ID: d8a51237-4fcc-4171-8071-a391da0be361

Retrieval Hint: "FM cockpit 314 vessel narrow layout rail zone overflow"