Claude driver: explicit model slug bypasses ANTHROPIC_DEFAULT_* mapping; worktree mode not honored (sessions run in live checkout)

Found while evaluating T3 Code (Alpha 0.0.28, macOS) with a Claude provider pointed at
OpenRouter per the docs (docs/providers/claude.md, "I Want To Use OpenRouter").
Three related issues:

1. Model picker stores explicit slugs, so ANTHROPIC_DEFAULT_*_MODEL mapping never applies

The docs suggest mapping Claude Code's model roles via env vars
(ANTHROPIC_DEFAULT_SONNET_MODEL=moonshotai/kimi-k3 etc.). However, the picker persists an
explicit versioned slug — state.sqlite modelSelection shows e.g.
{"model":"claude-sonnet-4-6", ...} — which Claude Code passes through verbatim. The
DEFAULT_* vars only map aliases (sonnet), so the mapping silently never fires: our
"Kimi" provider ran a real claude-sonnet-4.6 via OpenRouter ($ on the wrong model, easy to
miss). Interestingly CLAUDE_CODE_SUBAGENT_MODEL did apply — subagent calls went to Kimi
while the main thread ran Sonnet, which makes the mixed billing extra confusing.

Workaround we found: typing the full slug (moonshotai/kimi-k3) into the model-picker
search creates a custom entry that is passed through correctly.

Suggestion: either resolve picker selections through the provider's env mapping, or update
the OpenRouter docs section to recommend custom-slug entries instead of ANTHROPIC_DEFAULT_*.

2. "Local checkout" default writes into the live repo

Expected for the mode, but as a default it surprises: our first thread modified the real
working tree (untracked files in the user's main checkout). Consider defaulting new threads
to worktree mode, or a first-run hint.

3. Worktree mode selected but not honored

With New worktree explicitly selected (branching from a chosen ref), T3 created the
worktree (~/.t3/worktrees/<repo>/t3code-<id> on the right base) — but the Claude session
still launched with cwd = the project's live checkout (provider_session_runtime shows
"cwd": "<live repo path>"). The worktree stayed empty; all edits landed in the live repo
again. Reproduced on Alpha 0.0.28 with the Claude driver.

Happy to provide state.sqlite excerpts or logs. Thanks — the UI itself is genuinely nice.

🤖 Generated with Claude Code

Start with the model picker, docs/providers/claude.md, and the provider_session_runtime entry point, reproducing the explicit model mapping and selected-worktree cases described for Alpha 0.0.28. Done means mapped model aliases behave as documented, the selected worktree is used as the Claude session cwd, and local-checkout behavior is addressed or clearly surfaced to users.