DO NOT MERGE

Summary:
Adds a fallback normalizer that translates VSCode-LM <function_calls>…</function_calls> into native … tool XML. Zero behavior change for already-correct native XML; preserves inner byte-for-byte; default ON.

Integration points:

• Streaming pre-parse in AssistantMessageParser.processChunk()
• Non-stream at start of parseAssistantMessage() and parseAssistantMessageV2()
• Presentation metadata via presentAssistantMessage text branch

New module:

• FunctionCallsStreamingNormalizer with FunctionCallsStreamingNormalizer.process() and normalizeFunctionCallsXml()

Behavior:

• Strip <function_calls> container
• Map … → … only for known ToolName; unknown tools pass-through
• Streaming path uses small tail buffer, 1MB guard, and a stack; idempotent; never mutates

Telemetry:

• function_calls_normalized (boolean), toolNamesEncountered (set), modelId — minimal, non-PII

Tests:

• Updates in AssistantMessageParser.spec.ts and parseAssistantMessage.spec.ts
• Cases: single and multiple invokes, unknown tool preserved, multi-file args preserved byte-for-byte
• Existing suites remain green

Rollout:

• Enabled by default with light telemetry; can be disabled via experiment/provider state if needed

Risks/Mitigations:

• Mis-detection or malformed XML → rewrite only on full tokens; guarded stack; pass-through fallback

Acceptance:

• function_calls inputs execute equivalently to native XML; args preserved; no regressions.