fix: Delete an unnecessary callback, fix default log level

[grahamking]

The callback was only for rand algorithm to provide a slightly different log
message.

Changed the default log level to be info. Previously we had it as info for
specific crates but no default, so other crate's logs were discarded.

Reviewed-by: Cursor:Grok 4.6 xhigh

Signed-off-by: Graham King grahamk@nvidia.com

Summary by CodeRabbit

• Observability
  • Routing logs now present algorithm, target, confidence, and routing tier in structured fields for clearer diagnostics.
  • Default informational logging is broadened across the service while keeping OpenTelemetry messages limited to warnings.
• Maintenance
  • Removed legacy decision-message customization from fall-through and random routing behavior, simplifying routing configuration without changing routing outcomes.

[github-actions]

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[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 0cf6439 and 625a894.

📒 Files selected for processing (3)

• crates/libsy/src/algorithms/fall_through.rs
• crates/libsy/src/algorithms/rand.rs
• crates/switchyard-server/src/observability.rs

💤 Files with no reviewable changes (1)

• crates/libsy/src/algorithms/rand.rs

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Walkthrough

The change removes configurable decision-reason callbacks from routing algorithms, replaces formatted routing messages with structured tracing fields, and broadens the default server log filter to global info.

Changes

Routing logging cleanup

Layer / File(s)	Summary
FallThrough decision logging and random routing crates/libsy/src/algorithms/fall_through.rs, crates/libsy/src/algorithms/rand.rs	FallThrough no longer stores or configures decision-reason callbacks. Routing logs use structured target, confidence, and routing-tier fields. Random retains classifier wiring without custom reason generation.
Default tracing filter crates/switchyard-server/src/observability.rs	The default filter uses global info logging and retains the opentelemetry=warn override.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 625a8

The PR removes an unnecessary callback and makes the default logging level more inclusive; no actionable merge-blocking risk remains beyond normal checks and review.

Poem

I’m a rabbit hopping through the logs,
With tidy fields instead of fogs.
No callback carrots in the queue,
Targets and confidence shine through.
Global info guides the way—
Thump, trace, and route all day!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes both main changes: removing the unnecessary callback and correcting the default log level.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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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