Summary

• preserve config validation and JSON errors through HTTP middleware as client-visible 400 responses
• format SDK-wrapped config errors in TUI bootstrap aggregation so invalid config output includes the file and invalid path
• deduplicate identical startup failures and list the affected startup requests once
• document the recommended typed domain error -> declared HTTP API error -> shared CLI/TUI formatter pattern
• add regression coverage for TUI aggregation and HTTP error middleware

Verification

• bun run test -- test/cli/cmd/tui/aggregate-failures.test.ts test/server/httpapi-error-middleware.test.ts test/cli/error.test.ts
• bunx oxlint packages/opencode/src/cli/error.ts packages/opencode/src/server/routes/instance/httpapi/middleware/error.ts packages/opencode/src/cli/cmd/tui/context/aggregate-failures.ts packages/opencode/test/cli/cmd/tui/aggregate-failures.test.ts packages/opencode/test/server/httpapi-error-middleware.test.ts
• bun typecheck
• OPENCODE_DISABLE_AUTOUPDATE=1 bun dev /var/folders/dd/5fz89drs5p9_r0fk7rwqqnbr0000gn/T/opencode/issue-27056-bad-config
• bun turbo typecheck

Fixes #27056