feat(routing): unified structured Selected-worker INFO log across all router modes

[nnshah1]

Summary

Every router-mode worker selection now emits one consistent, structured, info-level "Selected worker" log, so routing decisions are visible without flipping DYN_LOG. Previously the modes were inconsistent — RoundRobin/Random/LeastLoaded logged at trace, P2C at debug, DeviceAwareWeighted and KV at info but with ad-hoc fields.

Unified schema

info!(router_mode = "<mode>", worker_id = <id>, candidate_count = <n>, load = <load-if-applicable>, … , "Selected worker: …")

Per mode:

• RoundRobin / Random / LeastLoaded — promoted trace! → info! with structured fields (LL also logs load).
• PowerOfTwoChoices — debug! → info!, retaining the candidate detail (candidate_a/b, loads); logs once per selection including the single-candidate path.
• DeviceAwareWeighted — re-fielded to the common schema, keeping endpoint / is_cpu.
• KV — kept the existing info! messages, added structured fields (router_mode, worker_id, worker_type, dp_rank, logit, block counts).
• Direct — added an info! at dispatch (router_mode="direct", worker_id; no candidate_count/load since the worker is caller-supplied).

Log aggregators can now grep/filter on router_mode / worker_id / load uniformly across all modes for imbalance analysis.

Test

cargo check / fmt / clippy clean on dynamo-runtime + dynamo-kv-router.

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• Chores
  • Enhanced observability and structured logging for worker selection in router components, providing more detailed metrics and context for monitoring and troubleshooting purposes.

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between a95e0b1 and 1084d0f.

📒 Files selected for processing (2)

• lib/kv-router/src/scheduling/selector.rs
• lib/runtime/src/pipeline/network/egress/push_router.rs

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Walkthrough

This PR enhances observability in router worker selection by converting formatted log messages to structured tracing::info! logs across KV and Push routers. Changes add explicit fields for worker identity, load metrics, and selection strategy details while elevating logging from trace/debug to info level for better visibility.

Changes

Router Selection Observability

Layer / File(s)	Summary
KV Router selection logging lib/kv-router/src/scheduling/selector.rs	DefaultWorkerSelector::select_worker now emits structured tracing::info! logs in both decode and non-decode paths with router_mode = "kv" and explicit fields for worker identity (worker_id, worker_type, dp_rank, logit) and cache metrics (host_pinned_blocks, disk_blocks, effective_cached_blocks).
Push Router selection logging lib/runtime/src/pipeline/network/egress/push_router.rs	All worker selection methods (p2c_select_from single/multi-candidate, round_robin, random, direct, device_aware_weighted, least_loaded) now emit consistent tracing::info! "Selected worker" logs (elevated from prior trace level) with explicit fields for selected worker id, candidate count, and current load.

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description covers the change summary and details but lacks the required 'Related Issues' section with either a linked issue or confirmation of no related issue.	Add the 'Related Issues' section from the template; either link to a related issue with 'Closes #XXXX' or check the 'Confirmed — no related issue' box.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: unified structured logging for worker selection across all router modes.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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