fix(opencode-excalidraw): canonicalize sketchi api base to www

[anand-testcompare]

Summary

• canonicalize plugin API base from https://sketchi.app to https://www.sketchi.app
• add normalization so SKETCHI_API_URL=https://sketchi.app is rewritten to www
• update plugin README default API base
• add regression test covering auth device-start URL canonicalization

RCA

• sketchi.app issues a 307 redirect to www.sketchi.app
• in plugin/runtime flows, auth is not reliably preserved across that redirect
• resulting backend failures surfaced as diagrams.threadRun failed (UNKNOWN)

Validation

• cd packages/opencode-excalidraw && bun run test (29 pass)
• bun x ultracite check packages/opencode-excalidraw/src/index.ts packages/opencode-excalidraw/src/index.test.ts packages/opencode-excalidraw/README.md (pass)
• manual repro:
  • POST https://sketchi.app/api/diagrams/thread-run could fail
  • POST https://www.sketchi.app/api/diagrams/thread-run succeeds

[vercel]

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Project	Deployment	Actions	Updated (UTC)
sketchi-web	Ready	Preview, Comment	Mar 2, 2026 6:49pm

[github-actions]

Browserbase Replays

• Session 6caa4d8c-5766-49cc-9901-3b6ff3fc837b (scenario: visual-sanity.ts): replay | debug
• Session 7f02432b-da3c-437e-bae7-d4b1071d9294 (scenario: auth-gates.ts): replay | debug
• Session be228d1c-ad94-408e-b226-334f0a8abff0 (scenario: opencode-web-continuity.ts): replay | debug
• Session 7e7b7b49-5809-4111-b0e4-d26ee6e26b47 (scenario: diagram-studio-happy-path.ts): replay | debug

Workflow run: 22590725982