Keep Advanced collapsed after a draft fail and name the CTA blocker

[TheGreatAxios]

Fixes CL-6751

Stacked on CL-6749. A failed Myra draft already shows a consumer sentence and refId; this change stops that failure from silently opening Advanced, puts the blocker on the disabled primary instead of "Get started", and stops model help from claiming Myra will pick one after drafting already failed.

• Draft failure keeps Advanced collapsed
• Disabled primary names the blocker (Open Advanced and write a system prompt to continue.)
• Model help after a failed draft: workbench default, not "Myra picks one"
• CL-6749 envelope/refId rendering is unchanged

[TheGreatAxios]

Self-review

Verdict: the change is minimal, correctly scoped to CL-6751 (keep Advanced collapsed after a failed draft, name the blocker on the disabled primary, drop the stale "Myra picks one" model help), and matches AGENTS.md conventions. No defects found; no code changes made.

• Advanced stays collapsed on draft failure (setAdvancedOpen(true) removed from the catch path) — CONFIRMED-FIXED (already correct in the PR as submitted; nothing further to change).
• Disabled primary now shows blocked ?? "Get started" instead of a separate helper paragraph — DISMISSED: matches the stated design intent (disabled label names the blocker) and is covered by the updated tests.
• Model help copy swaps "Myra picks one" for the workbench-default sentence once draftFailed is true — DISMISSED: correct, verified against the test asserting "Myra picks one" is absent post-failure.
• exactOptionalPropertyTypes, bare catches, as T on untrusted input, fallbacks-beside-new-paths: none introduced by this diff.
• Comments were updated to describe the new "keeps Advanced collapsed" behavior rather than restating code — fine.

Targeted tests run:

• bun test test/create-agent-panel.test.tsx (from apps/web) — 11 pass, 0 fail.
• bun run typecheck — clean.

No commits pushed; nothing to fix.

[linear-code]

CL-6751