feat(models): add optional Pricing field to ModelInfo

[manojp99]

🔄 Updated per triage feedback (2026-06-30)

Two commits added addressing the "Updated Triage — PR Branch Review" from issue microsoft-amplifier/amplifier-support#295:

refactor(models): drop Pricing.as_of and tighten schema (1a94515)

• Removed the speculative as_of: date | None field from Pricing — no consumer needed it, and dropping it eliminated the json.dumps(model_dump()) serialization hazard the triage flagged (Medium docs: update TOOL_CONTRACT.md with current ToolResult schema #1) and the "as_of always None" gap (Medium fix: improve MountPlanValidator test coverage and remove dead code #2) as byproducts.
• Added ISO 4217 currency validator (^[A-Z]{3}$) — addresses triage Medium feat: add debug/raw LLM events and document orchestrator:complete requirement #6.
• Added docstring note that Pricing uses float because it's display-only, and per-turn accounting uses Usage.cost_usd (Decimal) — addresses triage Medium Add MODULES.md community module catalog #4.
• Added round-trip test for Pricing.model_dump() + json.dumps and currency validation.

feat(models): propagate Pricing through Rust bridges + guest crate (cb28489)

• Added native Rust Pricing struct and pricing: Option<Pricing> field on Rust ModelInfo (crates/amplifier-core/src/models.rs).
• Added pricing_json string field on the proto ModelInfo at tag 7 (mirrors the existing defaults_json pattern at tag 6). Regenerated src/generated/amplifier.module.rs via build.rs.
• Extended src/generated/conversions.rs to round-trip pricing between native and proto structs in both directions. Parse failures return None (no synthetic default Pricing).
• Added parse_pricing_json helper in src/bridges/grpc_provider.rs and threaded it through list_models() — addresses the HIGH item in the triage (gRPC bridge silently dropping pricing).
• Added duplicated Pricing + field in crates/amplifier-guest/src/types.rs — closes the WASM guest-side gap the triage did not originally identify, but which is required for WASM providers to populate pricing at all.
• src/bridges/wasm_provider.rs requires no changes — it deserializes directly into native ModelInfo and picks up the new field via #[serde(default)].
• Rust unit tests for parse_pricing_json, updated equivalence_tests.rs, and new test_model_info_pricing_field in bindings/python/tests/test_schema_sync.py.

Verification results

• Python: 6/6 pricing/model_info tests pass; ruff/pyright clean on touched files (pre-existing issues elsewhere are documented, not fixed).
• Rust: cargo build --workspace regenerates proto cleanly; cargo test -p amplifier-core --lib 454/454 pass; cargo test -p amplifier-guest --lib 94/94 pass; clippy clean on amplifier-core and amplifier-core-py. Full-workspace cargo test hangs on unrelated wasm_* and sha256_* tests — these do not touch pricing code paths.
• Cross-language: pytest bindings/python/tests/ 370/370 pass including the new pricing test.

Design decisions locked

• Proto shape: string blob (pricing_json) mirroring defaults_json, not a nested message Pricing. Discussed in the triage response; the string-blob pattern is consistent with existing precedent and can be migrated to a nested type later without a breaking change.

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What

Adds an optional Pricing field to ModelInfo so providers can surface
per-model pricing (input/output/cache rates per million tokens, currency,
and an optional as_of date) through /v1/models.

Why

Today HTTP-bridge applications (e.g. amplifier-app-opencode) hand-maintain
their own pricing tables because pricing isn't part of model info on the
wire. This forces drift whenever provider pricing changes and leaves
end-users seeing stale cost estimates. Filed as
microsoft-amplifier/amplifier-support#295.

The fix is to expose the pricing data the provider modules already
maintain internally (each has a _RATES dict used for per-turn cost
accounting) through the public ModelInfo contract. No new source of
truth — we're promoting an existing one.

What's in this PR

• New Pricing pydantic model in python/amplifier_core/models.py
  • input_per_million, output_per_million (required floats)
  • cache_read_per_million, cache_write_per_million (optional)
  • currency (defaults to "USD")
  • as_of (optional date for staleness tracking)
• Optional pricing: Pricing | None = None field on ModelInfo (default None — backwards compatible)
• Pricing exported via python/amplifier_core/__init__.py
• Smoke tests in tests/test_model_info_pricing.py covering round-trip serialization and the pricing=None case

Compatibility

Backwards-compatible. Existing providers that don't populate pricing
continue to work; the field is None by default. Existing consumers that
don't read pricing are unaffected.

Companion PR

Partner change in amplifier-module-provider-anthropic populates the new
field from the existing _RATES table: microsoft/amplifier-module-provider-anthropic#63

Validation

Validated end-to-end in a Digital Twin Universe environment with both
patches active:

• amplifier-core patch installed, Pricing importable, field present on ModelInfo
• AnthropicProvider.list_models() returns models with populated pricing
• ModelInfo.model_dump(mode="json") emits the expected wire shape
• Opus values (5.0 / 25.0 USD per million in/out) match the expected rate sheet

Scope

This is the minimum viable slice — amplifier-core schema change here,
companion amplifier-module-provider-anthropic change in the partner PR.
Other providers (openai, azure-openai, gemini, vllm, ollama) are
follow-up work and will land in separate PRs.