Add cross-provider protocol conformance canaries

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Problem

A model returning a short chat completion does not prove that it supports streaming, tool calls, structured JSON, multimodal input, the Responses API, or the Anthropic Messages bridge.

Scope

• Define a small provider/model conformance matrix for supported protocol features.
• Add bounded canaries for chat, streaming, tool calls, JSON output, vision where advertised, Responses API translation, and Anthropic Messages translation.
• Record feature-level verification separately from basic model health.
• Route feature-specific requests only to targets that have passed that feature or are explicitly pinned by the user.
• Preserve per-model failures and serving provenance in reports.
• Re-run canaries after model-ID or adapter changes.

Acceptance criteria

• Every advertised feature has a deterministic minimal canary and normalized expected result.
• Unsupported capability errors are not counted as provider availability failures.
• Streaming tests detect mid-stream resets and truncated clean-looking responses.
• Tool/JSON tests reject syntactically successful but semantically invalid output.
• Capability results are machine-readable and visible in model/status output.
• Canaries are quota-bounded and never send repository or user content.

Related: #1 and #6.