feat(frontend): connect-model drawer redesign + connect-gate rework

docs/design/connect-model-drawer/README.md

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+# Connect a Model drawer redesign
+
+Planning workspace for redesigning the agent playground's "Model & harness" section
+drawer after the claude.design prototype "Connect a Model Flow", with the product
+owner's final decisions applied (three sections, a "Use API key" / "Use subscription"
+credentials toggle, inline custom providers, an unsaved-changes guard, and a readable
+selection style for the shared SectionRail).
+
+Status: **planned, not implemented**. See status.md for open decisions.
+
+## Files
+
+| File | What it holds |
+| --- | --- |
+| [context.md](context.md) | Why the work exists, the owner's locked decisions, scope, and constraints (uncommitted in-flight changes, package layering, dark mode). Read this first. |
+| [research.md](research.md) | Verified code map with file/line citations, the confirmed `--ag-colorPrimaryBg` root cause, SectionRail blast radius, the extracted design prototype, and the hex → theme-token mapping. |
+| [design.md](design.md) | Component-level design: drawer structure, the SectionRail restyle, the ProviderCredentialsSection and its props, the CustomProviderForm extraction (with required package moves), the unsaved-changes guard, Advanced-tab removal, gating matrix, and final copy strings. |
+| [plan.md](plan.md) | Six implementation slices sized for Sonnet subagents, in dependency order, plus the dev-stack verification plan (light + dark). |
+| [status.md](status.md) | Source of truth for progress, the open decisions D1-D6, locked decisions, and next steps. Keep it updated. |
+
+## Quick orientation
+
+- Drawer host: `web/packages/agenta-entity-ui/src/DrillInView/SchemaControls/AgentTemplateControl.tsx`
+- Stateful core: `.../SchemaControls/agentTemplate/useModelHarness.tsx`
+- Shared rail: `web/packages/agenta-entity-ui/src/drawers/shared/SectionRail.tsx`
+- Secrets: `web/packages/agenta-entities/src/secret/`
+- Custom-provider form (extraction source): `web/oss/src/components/ModelRegistry/Drawers/ConfigureProviderDrawer/`
+- Design prototype: `Agenta onboarding flow redesign (1)/Connect a Model Flow.dc.html`

docs/design/connect-model-drawer/context.md

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+# Context: Connect a Model drawer redesign
+
+## What this project is
+
+Redesign the "Model & harness" section drawer in the agent playground's left config panel.
+The redesign follows the claude.design prototype "Connect a Model Flow" (saved at
+`Agenta onboarding flow redesign (1)/Connect a Model Flow.dc.html` in the repo root).
+
+The drawer today mixes model, harness, and credential concerns across two tabs plus a
+separate Advanced drawer. The redesign gives the drawer three clear sections (Harness,
+Model, Provider credentials), moves the connection-mode choice out of Advanced into the
+credentials section, lets users add custom providers inline without a nested drawer, and
+stops silently discarding unsaved edits on an outside click.
+
+## Why now
+
+The agent onboarding flow funnels new users into this drawer (the chat's
+"Set up credentials" banner opens it). Three problems hurt that flow:
+
+1. **Selection is unreadable.** The harness list's selected row shows only bold text in
+   light mode. Root cause: the shared `SectionRail` styles its active row with
+   `var(--ag-colorPrimaryBg)`, a token the theme generator never emits, so the background
+   is transparent (see research.md).
+2. **Credentials are scattered.** The API-key field hides behind a "Provider key" rail
+   tab keyed to the selected model, and the Agenta-managed vs self-managed choice hides in
+   the Advanced drawer. A user connecting their first key has to find both.
+3. **Silent data loss.** Clicking the scrim closes the drawer and throws away the draft
+   with no warning.
+
+## Product owner's decisions (final, locked)
+
+These came from the product owner and are not open for redesign. The plan must implement
+them as stated.
+
+1. **Harness section: no layout or behavior change.** The only change is the selection
+   styling of its list rows (the shared `SectionRail` recipe). The design's dropdown
+   harness picker is NOT adopted.
+2. **Provider credentials section** with a two-option segmented toggle:
+   **"Use API key" / "Use subscription"**.
+   - "Use API key": provider rail on the left (standard providers with colored logo
+     tiles, "+ Custom provider" pinned at the bottom), credential form on the right for
+     the selected provider.
+   - Custom providers render their form INSIDE the right pane (card content swap). No
+     nested drawer, no stacked drawers, no pixel shifts. The existing custom-provider form
+     logic must be extracted into a reusable component that both the old surfaces
+     (`ConfigureProviderDrawer`) and this pane share.
+   - **Key saves stay immediate** (per-provider save button writing the vault, as today
+     via `useVaultSecret` / `createStandardSecretAtom`). The drawer's footer Save commits
+     only the agent config draft (harness / model / mode). LOCKED.
+   - "Use subscription": the rail and key form disappear; the pane becomes one info card.
+     The toggle label says "Use subscription"; INSIDE the card the heading and language
+     are "Self-managed" (the harness signs itself in: a Claude Code or Codex subscription
+     OR any harness-side auth such as environment variables). Mention the self-hosting
+     requirement; show a "Not on cloud" badge when gated.
+   - The toggle is capability-gated via the harness catalog's `allowedConnectionModes`,
+     plus deployment gating on cloud.
+   - Selecting the mode here REPLACES the mode selector in the Advanced drawer. The
+     Agenta-managed/Self-managed `SectionRail` and the named-connection `Select` leave
+     Advanced entirely. Nothing mode-related remains in Advanced.
+3. **Model section is its own section**, separate from credentials. Recommended order
+   (flagged as a decision, default to it): Harness → Model → Provider credentials. When a
+   model is picked, auto-highlight its provider in the credentials rail.
+4. **Unsaved-changes guard.** If the draft is dirty and the user closes without Save or
+   Cancel (scrim click, X), show a confirm modal: save / discard / keep editing.
+5. **Copy alignment.** The "self-managed" wording (accurate beyond subscriptions) must
+   also be used in the harness capability descriptions and any docs this plan touches.
+
+## Not in scope
+
+- Key validation or test calls against providers.
+- Any other drawer sections (Instructions, Tools, MCP servers, Skills, Triggers).
+- The chat `ConnectModelBanner` (already fixed separately).
+- Layout changes to the harness section beyond selection styling.
+
+## Constraints
+
+- **Build on the current working tree.** The touched files carry uncommitted in-flight
+  changes (chat gate logic, `agentCreationPrefsAtom` capture, `providerKeySetupDoneAtom`,
+  the self-managed pill fix in `providerNeedsKey`). Never revert them.
+- **Keep the creation-prefs capture seam working.** `AgentTemplateControl.saveSection`
+  reads the connection mode from `draftConfig.llm` via `connectionFromConfig` when the
+  model-harness section saves. Moving the mode control between sections must not break
+  that read (it won't, as long as the mode keeps living at `config.llm.connection.mode`).
+- **Dark mode must work.** Every design hex maps to an `--ag-*` theme token. The palette
+  source of truth is `web/oss/src/styles/theme/palette.ts` plus the generator; never
+  hand-edit `theme-variables.css` or `antd-overrides.generated.ts`.
+- **Package layering.** The drawer lives in `@agenta/entity-ui`; it cannot import from
+  `web/oss`. Anything the pane needs from the app layer must move into a package or flow
+  through the `DrillInUIContext` bridge.