docs(libsy): update readme / quickstart

[messiaen]

What

update libsy reame

Why

The motivation — what problem does this solve, or which ticket does it close?

Closes #

How tested

• uv run ruff check . clean
• uv run mypy switchyard clean
• uv run pytest tests/ green
• Manual smoke (describe what was run)

Checklist

• One class per file; filename = snake_case of the primary class.
• New public symbols exported from switchyard/__init__.py.__all__ if intended for downstream use.
• Unit tests added for new components / bug fixes.
• README / --help updated if customer-facing surface changed.
• Commits signed off (Signed-off-by: Your Name <email>) per the DCO.

Notes for reviewers

Anything reviewers should pay extra attention to — risky paths, follow-up tickets, intentional trade-offs.

Summary by CodeRabbit

• Documentation
  • Updated Rust API documentation to support optional per-session state in algorithms.
  • Documented composed routing with the new FallThrough router and its processor/classifier building blocks.
  • Expanded the reference algorithm list to include FallThrough and SubagentOverride.
  • Clarified how context carries algorithm telemetry and session state.

[coderabbitai]

Walkthrough

The README updates Algorithm with generic per-session state, adds a default process_signals, documents Processor, Classifier, and FallThrough, and expands the referenced algorithm list and Context description.

Changes

API and routing documentation

Layer / File(s)	Summary
Generic Algorithm contract crates/libsy/README.md	Algorithm<S = ()> and Context<S> are documented with state bounds, a default no-op process_signals, and expanded Context state details.
FallThrough composition and references crates/libsy/README.md	Processor and Classifier traits, FallThrough construction, and the expanded algorithm reference list are documented.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Poem

A bunny reads the Rusty page,
With state tucked neatly in its cage.
Processors hop, classifiers call,
FallThrough welcomes one and all.
The README shines—what a haul!

🚥 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 accurately describes the documentation-focused README and quickstart updates in libsy.
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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[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@crates/libsy/README.md`:
- Line 380: Update the earlier LlmClassifier example comment describing Context
to remove the stale claim that correlation IDs and budgets are already carried,
keeping it consistent with the current Context fields documented nearby.
- Around line 201-214: Update the README quickstart’s trait-object guidance to
use Arc<dyn Algorithm<S>> so it supports stateful implementations such as
FallThrough with SharedState, while retaining the existing stateless
Algorithm<()> usage where appropriate.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 0c562fc7-c02d-4830-b2da-01920e50994e

📥 Commits

Reviewing files that changed from the base of the PR and between 239a413 and ff2540f.

📒 Files selected for processing (1)

• crates/libsy/README.md