Add stop reason

[chrisboulton]

Right now a stop based on max_tokens does not return the proper stop reason - we just report a gen stop, when we should actually be reporting length.

Summary by CodeRabbit

• New Features
  • Generation-completion events now optionally report why generation stopped: end of sequence, maximum token limit, stop text, or an unknown reason.
  • Existing integrations remain compatible when no stop reason is provided.
• Release
  • Updated the package version to 0.5.1.

[coderabbitai]

📝 Walkthrough

Walkthrough

The protocol adds an optional SeqStopReason to SeqGenFinish, supports known and unknown serialized values, and updates the crate version from 0.5.0 to 0.5.1.

Changes

Sequence stop reason support

Layer / File(s)	Summary
Sequence finish stop reason contract src/protocol.rs	SeqGenFinish gains an optional Serde-compatible stop reason, and SeqStopReason defines Eos, MaxTokens, StopText, and Unknown variants.
Crate version update Cargo.toml	The package version changes from 0.5.0 to 0.5.1.

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

Suggested reviewers: zackangelo

🚥 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 matches the main change: adding stop-reason handling to generation events.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch gen-stop-reason

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[coderabbitai]

Actionable comments posted: 1

🤖 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 `@src/protocol.rs`:
- Around line 140-152: Update SeqStopReason’s serialization/deserialization
handling to use custom string serde instead of #[serde(other)], mapping
recognized snake_case values to Eos, MaxTokens, and StopText and all unknown
values to Unknown. Preserve serialization of known variants and add tests
covering each known value plus an unrecognized value.

🪄 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: defaults

Review profile: CHILL

Plan: Pro

Run ID: c42fc778-645b-4fa1-81df-8cca55c5f396

📥 Commits

Reviewing files that changed from the base of the PR and between cf831ce and 812afb5.

⛔ Files ignored due to path filters (1)

• Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (2)

• Cargo.toml
• src/protocol.rs