feat: Add allow-custom-agent-models patch

[GMNGeoffrey]

Claude Code validates the model field in custom agent frontmatter (~/.claude/agents/*.md) against a hardcoded list of aliases (sonnet, opus, haiku, etc.). This prevents using arbitrary model names like "gemini-2.5-flash" or "oai@gemini-3-pro-preview".

This patch removes that restriction so that arbitrary model names pass through to the API. On its own this would cause API errors against the real Anthropic API, but it enables a useful workflow: running a local proxy (e.g. Claudish) that intercepts requests and routes non-Claude model names to appropriate backends with format translation.

Two locations are patched:

1. The Zod schema in UDD that validates against enum() is relaxed to accept any string.
2. The validation flag that gates whether the model field is included in the returned agent definition is changed to accept any non-empty string rather than only specific aliases. The search for this validation uses the captured list variable name from the Zod schema for robustness (the variable name has already changed across the few CC versions I tested).

Verified against real binaries: 2.1.58, 2.1.62, 2.1.69, 2.1.70.

The patch is opt-in (Features group, default: false). Enable with
allowCustomAgentModels: true in tweakcc config.

Summary by CodeRabbit

• New Features
  • Added an "Allow custom agent models" setting with a toggle in the Misc/Settings UI to permit arbitrary model names in custom agent frontmatter.
• Tests
  • Added test coverage validating the transformation and handling of various model-validation patterns.
• Integrations
  • Hooked the new setting into the patching flow so the permissive model handling is applied when enabled.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 03ba01e0-c065-4a8a-aead-9e7b8ff84f84

📥 Commits

Reviewing files that changed from the base of the PR and between af357f5 and 150130c.

📒 Files selected for processing (4)

• src/defaultSettings.ts
• src/patches/index.ts
• src/types.ts
• src/ui/components/MiscView.tsx

🚧 Files skipped from review as they are similar to previous changes (4)

• src/ui/components/MiscView.tsx
• src/types.ts
• src/patches/index.ts
• src/defaultSettings.ts

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📝 Walkthrough

Walkthrough

Adds a feature flag allowCustomAgentModels with config, type, default, UI toggle, a new code-transform patch writeAllowCustomAgentModels, tests for that patch, and registers the patch behind the new flag.

Changes

Cohort / File(s)	Summary
Configuration & Types src/defaultSettings.ts, src/types.ts	Adds allowCustomAgentModels: boolean to DEFAULT_SETTINGS.misc and MiscConfig type (default false).
Patch Implementation src/patches/allowCustomAgentModels.ts	New `writeAllowCustomAgentModels(file: string): string
Patch Tests src/patches/allowCustomAgentModels.test.ts	Adds Vitest suite covering multiple code patterns, minified names, brace-edge cases, false positives, and non-transform scenarios.
Patch Registration src/patches/index.ts	Registers new patch definition allow-custom-agent-models, imports writeAllowCustomAgentModels, and wires implementation to run when config.settings.misc?.allowCustomAgentModels is truthy.
User Interface src/ui/components/MiscView.tsx	Adds a toggle control wired to settings.misc.allowCustomAgentModels in the Misc settings UI.

Sequence Diagram

sequenceDiagram
    participant User
    participant UI as MiscView (UI)
    participant Config as Settings Config
    participant PatchSys as Patch System
    participant PatchFn as writeAllowCustomAgentModels

    User->>UI: Toggle allowCustomAgentModels
    UI->>Config: Update misc.allowCustomAgentModels
    Config->>PatchSys: Settings read during patch run
    Note over PatchSys: Evaluate enabled patches
    alt allowCustomAgentModels enabled
        PatchSys->>PatchFn: Run on matching files
        PatchFn->>PatchFn: Locate Zod enum model validation
        PatchFn->>PatchFn: Replace with string().optional() model validation
        PatchFn->>PatchFn: Replace restrictive includes/flag logic with permissive check
        PatchFn-->>PatchSys: Return transformed file content
        PatchSys-->>Config: Persist patch result / emit diff
    else disabled
        PatchSys-->>Config: Skip patch
    end

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• fix: make model customizations configurable and update models to latest #572: Adds a misc boolean setting and wires patch gating into src/patches/index.ts, matching the same pattern used here.

Suggested reviewers

• bl-ue

Poem

🐰 A tweak, a toggle, a tiny surprise,
Zod enums yield to stringy skies,
I hopped through code with glee and vim,
Now agents wear new model trim,
Hop—custom models, let them in! 🎉

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding a new patch feature to allow custom agent models.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[georpar]

Great feature; thank you!