[BUG] Auto mode missing from permission mode picker on Fable 5 (VS Code extension, Windows)

Summary

On the VS Code extension, auto mode does not appear in the permission mode selector when the session model is Fable 5. New sessions silently start in "Edit automatically" (acceptEdits) instead. Switching the model to Opus 5 on the same machine, same extension version, same settings makes Auto available again immediately.

Per the docs, Fable 5 is a supported model for auto mode on the Anthropic API, so this looks like the model-support check failing to recognize Fable 5 rather than intended behavior.

Environment

• Claude Code VS Code extension: 2.1.233
• Standalone CLI: 2.1.232
• OS: Windows 11 Pro 10.0.26200
• Signed in with a claude.ai account on a paid consumer plan (Anthropic API; not Bedrock/Foundry/Vertex)
• No managed settings file (C:\ProgramData\ClaudeCode\managed-settings.json absent)
• No defaultMode override in any project-level .claude/settings.json or .claude/settings.local.json

Steps to reproduce

1. In ~/.claude/settings.json, set:

``json
"permissions": { "defaultMode": "auto" }
``

1. Set the model to claude-fable-5[1m] (via /model).
2. Start a new session in the VS Code extension.
3. Open the permission mode selector.

Expected

Auto appears in the mode selector, and the session starts in auto mode per defaultMode.

Actual

Auto is absent from the selector entirely. The session starts in "Edit automatically" (acceptEdits). No error or explanation is shown.

Changing only the model to claude-opus-5[1m] and starting a new session restores Auto to the selector, with no other change to settings, extension version, or environment.

Why this looks like a bug

permission-modes.md states under the auto mode requirements:

Model: on the Anthropic API and Claude Platform on AWS, Claude Opus 4.6 or later, Sonnet 4.6 or later, or Fable 5.

So Fable 5 should qualify. The same page also says:

If Claude Code reports auto mode as unavailable, one of these requirements is unmet; this is not a transient outage.

Plan, organization, and provider requirements are all met here (paid consumer plan, no managed settings disabling it, Anthropic API), and the only variable that changes the outcome is the model. Auto mode was working on Fable 5 for this account until recently; I did not identify the exact version where it stopped.

Note the [1m] context variant is not the trigger: claude-opus-5[1m] offers Auto while claude-fable-5[1m] does not.

Impact

Sessions silently downgrade from auto mode to acceptEdits with no notification, so the first sign is unexpected permission prompts. Because the fallback is silent, it reads like an account or outage problem rather than a model-support check, which makes it hard to diagnose.