[None][fix] Restore CTX transfer progress when scheduling stalls

[peihu-nv]

@coderabbitai summary

Description

PR #17104 removed the disaggregated transfer admission limit and its per-iteration idle-progress collectives. When a context worker subsequently exhausted available KV capacity while sends were still in flight, no forward could run, so the normal nonblocking completion poll became unreachable. The completed sends continued pinning their KV blocks and the worker could stall indefinitely.

Keep unrestricted transfer admission, but restore a targeted blocking completion poll only when no request fits, no generation-init request is ready, and a context transfer is still in flight. The existing transfer-status path performs the required completion consensus and releases the pinned blocks; normal executor iterations retain the collective-free fast path.

Test Coverage

• Focused TestDisaggTransferIdleProgress suite passes: 11 passed. It covers the zero-fit/in-flight context-transfer condition and verifies that the existing blocking context-status poll is entered without restoring the removed WORLD or TP/CP entry collectives.
• Changed-file pre-commit hooks pass.
• Five independent 900-second MiniMax-M3 AgentX profiles pass on GB300 with one TP2 context worker and four TP4 generation workers: 885 warmup requests and 2,348 profiling requests completed with zero serving errors, timeouts, CUDA assertions, or OOMs. The repaired path was exercised 1,153 times.
• Ten additional matched stress replicas are in progress.

PR Checklist

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[peihu-nv]

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[tensorrt-cicd]

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PR_Github #64386 [ run ] completed with state SUCCESS. Commit: d0595c5
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[peihu-nv]

New PR aligned with main #17428