Handle model provider timeouts and errors

[KyleAMathews]

Fixes #4520.

Summary

• add default model-provider timeout/retry settings for Pi-backed agent runs
• classify provider failures into durable MODEL_PROVIDER_* error codes
• attach provider errors to the active run so the UI exits thinking and displays error_code + message inline
• preserve classified provider error codes in process-wake error rows
• add model provider error classification tests

Verification

• pnpm --filter @electric-ax/agents-mcp build
• pnpm --filter @electric-ax/agents-runtime typecheck
• pnpm --filter @electric-ax/agents-runtime exec vitest run test/model-provider-error.test.ts
• pnpm --filter @electric-ax/agents-runtime build
• pnpm --filter @electric-ax/agents-server-ui typecheck

[github-actions]

Electric Agents Desktop Builds

Build artifacts for commit 9cec07d.

Platform	Status	Artifact
macOS Apple Silicon	Passed	DMG
macOS Intel	Passed	DMG
Windows x64	Passed	Installer
Linux x64	Passed	AppImage / deb

Workflow run

[codecov]

Codecov Report

❌ Patch coverage is 73.11321% with 57 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.03%. Comparing base (cb6ae57) to head (9cec07d).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
packages/agents-runtime/src/pi-adapter.ts	54.54%	30 Missing ⚠️
packages/agents-runtime/src/outbound-bridge.ts	7.14%	13 Missing ⚠️
...ackages/agents-runtime/src/model-provider-error.ts	93.22%	8 Missing ⚠️
.../agents-server-ui/src/components/AgentResponse.tsx	0.00%	5 Missing ⚠️
packages/agents-runtime/src/process-wake.ts	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4521      +/-   ##
==========================================
+ Coverage   54.88%   55.03%   +0.14%     
==========================================
  Files         307      308       +1     
  Lines       34522    34715     +193     
  Branches     9871     9919      +48     
==========================================
+ Hits        18949    19104     +155     
- Misses      15554    15592      +38     
  Partials       19       19              

Flag	Coverage Δ
packages/agents	71.89% <ø> (ø)
packages/agents-mobile	84.09% <ø> (ø)
packages/agents-runtime	80.90% <74.87%> (-0.07%)	⬇️
packages/agents-server	72.80% <ø> (+0.04%)	⬆️
packages/agents-server-ui	5.89% <0.00%> (+<0.01%)	⬆️
packages/electric-ax	46.42% <ø> (ø)
typescript	55.03% <73.11%> (+0.14%)	⬆️
unit-tests	55.03% <73.11%> (+0.14%)	⬆️

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[github-actions]

Electric Agents Mobile Build

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