Fix Ask Mantosh modal background accessibility exposed by theme audit

Parent and blocking relationship

This bounded accessibility repair is a sub-issue of #72. It blocks completion of workflow repair #73 / PR #74 and therefore keeps recruiter-readiness PR #71 frozen.

Do not modify PR #71, its branch, head, labels, review state or draft state.

Repeated exact evidence

The unchanged browser contract failed on two consecutive PR #74 heads after the protected-path regression step itself passed:

1. Head 1a47d89bf1a2bacbc11fe6d9992709ec04d7b759: audit job 105915826656, 21/22 browser tests, artifact 10586459433.
2. Head 80930992c36c4a312f094d2947cfa8f11264e8eb: audit job 105916902948, 21/22 browser tests, artifact 10585514158, digest sha256:c6ead71aa8730167e46aeeab09a37c938a8fb4e96c8922d01f20c1360423c727.

Both failures are the unchanged desktop test Ask Mantosh errors remain readable in every appearance mode. Axe reports serious color-contrast violations on project-card content behind the open dialog/backdrop.

Diagnosis to verify

The live implementation declares the panel role="dialog" aria-modal="true" and renders a dark blurred backdrop. Opening it only reveals the panel/backdrop and adds body.ask-mantosh-open; it does not make the header, main content or footer mechanically inert and does not establish a complete focus boundary.

The screenshot and computed colors show that Axe is evaluating visible dimmed page content behind the modal. Strategy's current inference is that the modal visually deactivates the background without actually making it inactive for keyboard and accessibility semantics.

The producer must confirm or correct this diagnosis from the exact artifact and live code before implementation.

Required repair

• Continue from current main on a dedicated new branch and draft PR; do not add this unrelated product repair to PR #74.
• Preserve the existing accessibility and browser tests unchanged.
• When Ask Mantosh opens, make all non-dialog page content mechanically inactive to keyboard, pointer and accessibility navigation while leaving the dialog operable.
• Keep focus inside the modal while open.
• Preserve Escape, backdrop click, minimize/close behavior and exact restoration of previous focus and prior element state.
• Preserve every appearance mode, responsive behavior, conversation state and current visual design unless a minimal product change is required for the accessibility contract.
• Remove inertness and restore the page deterministically on every close path.
• Run the unchanged browser suite on desktop and mobile plus full repository verification.
• Require exact-head audit/floor success and direct browser evidence before review.

Test-integrity boundary

Do not weaken, skip, exclude, delay, mock away or scope Axe to the dialog merely to hide background violations. Do not lengthen waits and call the defect fixed. Do not edit existing browser/protected tests under this task. If implementation proves an existing test contract itself is wrong, stop and use the protected-test-change authority path with independent review.

Roles and boundaries

• Producer: Claude, bounded product repair only after publishing a short exact-file plan.
• Independent reviewer: Codex after producer self-review and Strategy exact-head verification.
• Merge authority: founder only.

Do not write to main, change PR #71, change PR #74, merge, mark ready, deploy, publish, modify provider configuration, add dependencies without Strategy approval, or broaden this into a redesign.

Acceptance criteria

• Exact diagnosis is published before implementation.
• Dedicated draft PR against current main.
• Background content is mechanically inactive while the modal is open and restored on every close path.
• Keyboard focus cannot escape behind the modal.
• Existing accessibility/browser tests are unchanged.
• The existing appearance-mode error test passes without altered waits, exclusions or Axe scope.
• Full browser suite passes desktop and mobile.
• Exact-head audit and floor are green.
• Producer self-review and direct artifact evidence are append-only.
• Strategy exact-head verification is clean.
• Codex independent exact-head review is CLEAN.
• Founder alone decides and performs merge.

Start by inspecting the live Ask Mantosh dialog implementation and the unchanged browser test “Ask Mantosh errors remain readable in every appearance mode,” then review the linked audit artifact for the reported background violations. Done means background content is mechanically inactive, focus remains in the dialog, all close paths restore state, and the unchanged desktop/mobile browser suites and full verification pass.