Propagate nested rollout trace lineage

[jdchawla29]

Summary

• keep telemetry context as simple trace-header storage
• propagate the active trace across MCP and decode inbound MCP trace metadata at the MCP boundary
• derive local and hosted rollout parentage when a rollout starts, keeping nested rollouts on distinct child traces
• send child and parent headers through SDK gateway clients and Claude Code gateway requests, prevent equivalent-ID self-parenting across standard UUID forms, and omit invalid hosted parent IDs

Verification

• UV_CACHE_DIR=/private/tmp/hud-python-uv-cache uv run --extra dev pytest -q hud/agents/tests/test_tool_agent.py hud/agents/tests/test_claude_sdk_agent.py hud/utils/tests/test_gateway.py hud/eval/tests/test_job.py hud/eval/tests/test_rollout.py hud/eval/tests/test_hosted.py hud/telemetry/tests/test_instrument.py hud/tests/test_trace.py hud/agents/tests/test_trace.py hud/eval/tests/test_file_tracking_observer.py (202 passed)
• UV_CACHE_DIR=/private/tmp/hud-python-uv-cache uv run --extra dev --extra train ty check on changed source files
• UV_CACHE_DIR=/private/tmp/hud-python-uv-cache uv run ruff format and ruff check on all changed files

---

Note

Medium Risk
Touches trace context, platform reporting, and gateway/MCP headers across eval and agents; behavior changes are mostly additive but affect how nested and hosted rollouts are attributed.

Overview
Adds parent–child trace lineage so nested rollouts and downstream calls stay linked in HUD telemetry and on the platform.

Context and propagation: set_trace_context now accepts an optional parent_trace_id and exposes Trace-Id plus X-HUD-Parent-Trace-Id via get_trace_headers(). The inference gateway and Claude SDK agent (gateway MCP headers, ANTHROPIC_CUSTOM_HEADERS, Windows remote env via base64 JSON) forward those headers. Outbound MCP tool calls attach hud/trace-id in request meta; get_mcp_trace_id() reads it (or trace-id HTTP header) on the server side.

Rollouts: Local rollout and hosted submit derive the parent from the ambient trace or inbound MCP context, bind the child trace with that parent, and report parent_trace_id on trace enter / rollout submit. Self-parenting is dropped when parent and child normalize to the same id; hosted submit also omits parents that fail canonical UUID formatting.

Other: normalize_trace_id prefers uuid.UUID parsing before the namespaced fallback.

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Review	Status	Commit	Review trigger
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