Switch desktop agent from Opus to Sonnet 4.6

[atlas-agent-omi]

One-line change: DEFAULT_MODEL in ACP bridge from claude-opus-4-6 → claude-sonnet-4-6.

Why: 16 desktop agent users burning $291/user/month on Opus. Projected $4.6K/month. Sonnet handles agentic tool use equally well.

Savings: ~$4.2K/month (~70% reduction on this key).

[greptile-apps]

Greptile Summary

This PR swaps the DEFAULT_MODEL constant in the ACP bridge from claude-opus-4-6 to claude-sonnet-4-6, and removes the now-redundant SONNET_MODEL constant alongside its pre-warm entry. The change affects two code paths: the session pre-warm fallback list (line 596) and the per-query model resolution (line 681). Both are updated correctly and consistently.

Key changes:

• DEFAULT_MODEL updated to "claude-sonnet-4-6" — all queries without an explicit msg.model will now route to Sonnet
• SONNET_MODEL constant removed — it was only referenced in the pre-warm list, so removal is safe
• Pre-warm list reduced from [DEFAULT_MODEL, SONNET_MODEL] (two sessions) to [DEFAULT_MODEL] (one session) — correct since Sonnet is now the single default
• Clients that explicitly pass msg.model = "claude-opus-4-6" are unaffected; the fallback only applies when msg.model is absent

Issues found:

• Minor: the replacement comment on line 582 describes the old SONNET_MODEL as an "Opus fallback," which reverses the actual relationship — both models were pre-warmed independently, not as fallbacks for each other

Confidence Score: 5/5

• Safe to merge — the one-line model swap is correct and all usages of DEFAULT_MODEL are consistently updated.
• The change is minimal and surgically correct: DEFAULT_MODEL is used in exactly two places (pre-warm fallback and query fallback) and both are handled by this PR. The removed SONNET_MODEL constant had no other references. The only finding is a P2 comment wording nit that doesn't affect runtime behavior.
• No files require special attention.

Important Files Changed

Filename	Overview
desktop/acp-bridge/src/index.ts	Swaps DEFAULT_MODEL from claude-opus-4-6 to claude-sonnet-4-6 and removes the now-redundant SONNET_MODEL constant + its pre-warm entry. Both usages of DEFAULT_MODEL (pre-warm fallback and query fallback at line 681) are correctly updated. Minor comment wording issue on line 582.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Query arrives from Swift] --> B{msg.model set?}
    B -- Yes --> C[Use msg.model\ne.g. claude-opus-4-6]
    B -- No --> D[Use DEFAULT_MODEL\nclaude-sonnet-4-6]
    C --> E[resolveSession / session/new]
    D --> E
    E --> F[session/set_model]
    F --> G[session/prompt]

    H[preWarmSession called] --> I{sessionConfigs provided?}
    I -- Yes --> J[Warm configured sessions]
    I -- No --> K[Warm DEFAULT_MODEL only\nclaude-sonnet-4-6]
    J --> L[session/new + session/set_model]
    K --> L

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_{Reviews (2): Last reviewed commit: "Fix Greptile: remove duplicate SONNET_MO..." | Re-trigger Greptile}

[atlas-agent-omi]

/review

[atlas-agent-omi]

@greptileai