Rewrite the Studio visual contract and align the shell to it

Traceability

• Spec ID: studio-visual-language-beta
• Status: Implemented

Intent

The alpha visual contract was structurally right and materially wrong. Its docked-workbench model, evidence roles, and interaction rules held up; its rendered values did not. Five near-identical blue-blacks separated only by solid mid-gray rules, a 2px radius on every control, a single 32px display size above an otherwise 12–14px page, and semibold as the default weight produced a surface that reads as an unfinished wireframe rather than a precision instrument.

This spec replaces the alpha token set with beta and migrates packages/harness-studio onto it. The roles do not change — blue is still the only interaction hue, violet still means Candidate, the categorical scale still carries no judgement — but their values, the shape scale, the type scale, and the depth model do. It also repairs the conformance gaps the new values exposed: a landing-page hero on Overview, an embedded pane rendering its own light palette inside the dark shell, empty lanes repeated for every unevidenced scope, one boundary claim restated in three chrome slots, and comparison lanes borrowing the interaction and Candidate hues to mean nothing more than "left" and "right".

Acceptance Scenarios

• AC-1: DESIGN.md publishes a beta token set: an ordered surface ramp, alpha hairlines, a control radius that reads as a deliberate shape, a two-step depth model whose steps both belong to transient surfaces, a type scale with per-role tracking and a usable middle (subhead), and a medium weight. Every foreground/background pair in both themes meets WCAG 2.2 AA, measured against the busiest surface each foreground lands on.
• AC-2: packages/harness-studio renders entirely from those tokens. The two owned stylesheets contain no literal color, and no docked pane, row, button, tab, table, or empty state carries a shadow.
• AC-3: Overview leads with the decision and one primary action, not a display headline filling a region above rows a third its size. It carries no duplicate of the sidebar navigation and no second panel that is a filtered view of the first. Each input row names what the input unlocks and, when absent, the flag that supplies it.
• AC-4: The embedded Inspector workbench inherits Studio's active theme. Switching Studio to light or dark changes that pane with the rest of the shell, and its metric labels stay whole words at every layout mode. Only theme literals are inherited: the report keeps its own shape and metric scale, so adopting Studio's radii does not reshape a surface this spec does not migrate.
• AC-10: Every interactive control keeps an accessible name at every layout mode. A toolbar label hidden to save width is clipped, not removed, and a control strip that hosts a popup menu is never made a scroll container.
• AC-5: A scope that retained no prompt, tool call, or commit collapses to its title row instead of rendering three empty lanes.
• AC-6: A boundary claim appears once, in the pane that owns it. No sentence is placed in a column narrow enough to wrap two words per line.
• AC-7: Session comparison lanes use neutral surfaces. Neither the interaction blue nor the Candidate violet is used as a container color for lanes the evidence does not rank.
• AC-8: Numeric table columns are marked, not inferred from column position: headers align with their values, and text columns stay left-aligned.
• AC-9: At 1440×900, 1024×768, and 390×844, in both themes, every Studio surface renders with no document-level horizontal overflow, no console or page errors, and no text below the 12px floor.

Non-Goals

• Migrating the standalone Harness Inspector report (scripts/harness-inspector/ui/) onto the beta values. It still ships the alpha palette as a literal copy so it opens offline; Studio now overrides its presentation only where the embedded pane is visibly wrong. The report remains a migration target.
• Changing Studio's information architecture. The Workspace -> Sessions -> Detail / Compare -> Artifacts model is unchanged.
• Adding product surfaces, evidence semantics, or runtime capability.

Plan

1. Define the beta palette and verify AA contrast for every foreground/background pair in both themes before writing any CSS.
2. Rewrite src/app/styles/tokens.css as the single runtime source of the new values, keeping the existing custom-property names so the two feature stylesheets migrate without a rename pass.
3. Rewrite the visual sections of DESIGN.md — front-matter tokens, theme direction, typography, color, spacing/shape/depth — and record the conformance rules the migration surfaced.
4. Repair the conformance gaps: Overview lead and input inventory, embedded theme inheritance, unevidenced scope rows, duplicated boundary claims, comparison lane color, numeric column marking, narrow-mode title priority.
5. Update the browser contract test's docked-region selectors and the assertions that pinned alpha sizing values.

Test and Review Evidence

• npx vitest run — 127 tests across 19 files pass.
• npx playwright test — 16 tests pass, including the rendered-contract assertions for docked shadows, the 12px type floor, document overflow, owned stylesheet count, and the wide/compact/narrow layout sweep.
• Contrast verification over the full beta palette: every foreground against every background surface, both themes, all pairs ≥ 4.5:1.
• Visual review against a real 100-Session workspace: 24 captures covering Overview, Sessions, Debugger, and Compare at 1440×900, 1024×768, and 390×844 in both themes, saved under .qoder/design-qa/studio-beta/. The capture run reported no console errors, no page errors, and no document overflow.

Risk

The token rewrite changes every Studio surface at once, including surfaces whose evidence this repository cannot produce locally (live AG-UI runs against a real adapter, provisioned Canvas viewers). Those paths are covered by the existing Playwright fixtures rather than by the real-workspace capture, so a regression there would surface as a test failure rather than in the review screenshots. Sizing tokens moved (title bar 40→44px, secondary pane 304→312px, control 30→32px), so any downstream layout that pinned the alpha numbers needs the same update the browser suite received.