#434 fix: detect Anthropic wire from the model adapter

Summary

Magic Context used providerID === "anthropic" to decide whether it could use empty-part sentinels. OpenCode makes that decision from the resolved model adapter instead:

model.api.npm === "@ai-sdk/anthropic"

This matters for custom providers. A Portkey gateway can use the Anthropic adapter under a provider id such as portkey. The gateway receives Anthropic-format messages, but Magic Context previously skipped the merged-reasoning strip. Anthropic can then reject a long session because a thinking block in the latest assistant message changed.

This change reads each model's resolved adapter from provider.list(). It enables the sentinel paths only for models on @ai-sdk/anthropic, including custom provider ids. The lookup is per model because a provider can mix adapters across its models.

Cache safety

• One capability is resolved for the whole transform pass and passed to every sentinel consumer
• A new custom-provider capability folds the m[0] baseline once before it changes served bytes
• An unresolved registry carries forward the prior answer only for the same model
• Provider-list lookups have a five-second limit and retry after a cooldown

Rust mode remains limited to the canonical anthropic provider. Its module applies its own provider-id checks. Pi does not use these OpenCode paths. Both limits are documented in A55 of docs/AUDIT-KNOWN-ISSUES.md.

Validation

• Verified a live opencode serve reports the custom Portkey Claude models with api.npm: "@ai-sdk/anthropic"
• Verified the shipped OpenCode binary filters empty parts in the @ai-sdk/anthropic adapter branch
• Added unit coverage for custom providers, mixed adapters, resolver states, execute-to-defer byte stability, and the one-time m[0] fold
• bun run typecheck, plugin lint, build, and the thinking-block e2e test pass
• packages/pi-plugin tests: 1027 pass
• packages/plugin tests: 4644 pass; 2 existing dreamer/verify tests fail because temporary test repositories inherit SSH signing without a key

I also ran the full e2e suite. It reports 9 failures. Each reproduces on unmodified master.

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Summary by cubic

Fixes Magic Context's empty-part sentinel gating so custom providers that use the @ai-sdk/anthropic adapter (e.g., Bedrock/Vertex gateways) no longer send thinking blocks Anthropic rejects. The gate now reads each model's resolved adapter from provider.list() instead of using providerID === "anthropic".

Bug Fixes

• Resolves the capability per model because a provider can mix adapters across its models.
• Normalizes persisted sentinels when the model's resolved capability changes, so stale empty parts or placeholders don't survive a switch.
• Memoizes successful registry loads and retries after a cooldown, with a five-second limit.
• Records the widened capability in the m[0] upgrade identity so it folds exactly once, preserving byte stability.
• Keeps Rust mode limited to the canonical anthropic provider and documents the limitation in A55.

Confidence Score: 5/5

The PR appears safe to merge; the latest changes correctly normalize persisted sentinels across model capabilities without bypassing the existing materialization gates.

No actionable new defects or outstanding previous findings were established. Model recovery seeds the shared live-model map before hard-signal evaluation, keeping adapter capability resolution, model-change detection, and m[0] folding aligned.

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Transform pass starts] --> B[Resolve live model]
    B --> C[Load provider registry]
    C --> D{api.npm is @ai-sdk/anthropic?}
    D -->|Canonical or matching custom model| E[Enable empty sentinels]
    D -->|Other adapter| F[Use dropped placeholder]
    C -->|Temporarily unresolved| G{Same cached model?}
    G -->|Yes| H[Carry prior widened capability]
    G -->|No| F
    E --> I[Compare m0 adapter identity]
    F --> I
    H --> I
    I --> J{Provider-visible capability changed?}
    J -->|Yes, same known model| K[Materialize and persist new baseline]
    J -->|No| L[Replay frozen decisions]
    K --> L
    L --> M[Strip reasoning and normalize sentinels consistently]

_{Reviews (2): Last reviewed commit: "fix: normalize sentinels after model cha..." | Re-trigger Greptile}