Add 0050 example coverage: degrade mode and call-level retry

[chris-colinsky]

Summary

Fold proposal 0050's two new primitives into existing worked examples and their docs, rather than adding standalone demos.

• fan-out-with-retry gains a degrade failure posture alongside fail_fast and collect. FailureIsolationMiddleware wraps each fan-out instance as the outermost layer (retry stays inner), so an instance whose retries exhaust is caught and degraded to a placeholder result and the batch finishes intact. The demo env knob is renamed COLLECT_MODE to MODE (fail_fast / collect / degrade).
• chat-with-multimodal gains call-level complete(retry=RetryConfig(...)) on the respond node, retrying just the LLM wire call on transient categories. Its failure-handling rundown grows from three placements to four.

Each example's docs page is updated, and the middleware and LLMs concept pages get backlinks to the new demonstrations.

Notes

• The fan-out degrade demo is behavior-only (no event observer): at the instance-middleware layer the FailureIsolatedEvent currently reports the engine's wrapper category rather than the originating cause. That fidelity question is tracked separately and does not affect the degrade behavior shown here.
• No src/ changes. Both 0050 primitives shipped already (in Add FailureIsolationMiddleware (proposal 0050) #149 / Add RetryConfig record for RetryMiddleware #150 / Add call-level retry to Provider.complete() #151); this is example and docs coverage only.

Validation

• ruff format / check, pyright, and pytest tests/test_examples_smoke.py (13/13) pass; mkdocs build is clean.
• Both examples verified live: fan-out in fail_fast and MODE=degrade (the sentinel degrades to a placeholder, the rest summarize, no error block), and the chat demo across its four turns.

[Copilot]

Pull request overview

Updates existing worked examples and documentation to demonstrate proposal 0050’s two primitives (failure isolation “degrade” posture and call-level retry) without adding new standalone demos.

Changes:

• Extend fan-out-with-retry with a new MODE=degrade posture using FailureIsolationMiddleware as outermost instance middleware, and rename the env knob from COLLECT_MODE to MODE.
• Extend chat-with-multimodal to use call-level retry via complete(retry=RetryConfig(...)) and update the failure-handling discussion accordingly.
• Add docs backlinks from middleware/LLM concept pages to the updated demonstrations.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
examples/fan-out-with-retry/main.py	Adds MODE handling and degrade posture via FailureIsolationMiddleware in instance middleware.
examples/chat-with-multimodal/main.py	Demonstrates call-level retry on complete(retry=...) and updates explanatory text/output.
docs/examples/fan-out-with-retry.md	Updates example docs for MODE (fail_fast / collect / degrade) and degrade behavior.
docs/examples/chat-with-multimodal.md	Documents call-level retry usage and expands failure-handling discussion.
docs/concepts/middleware.md	Adds backlink to the fan-out degrade composition demonstration.
docs/concepts/llms.md	Adds backlink to the chat example demonstrating call-level retry.

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