fix(libsy): put judge system prompt in instructions, not messages

[linj-glitch]

PR #204 refactored CapabilityJudge to a StructuredJudge type alias, but StructuredJudge::build_request inserts the system prompt into messages as a Role::System entry instead of LlmRequest.instructions. This silently reverted the fix from PR #195 and removed its test.

For OpenAI-compatible backends the wire output happens to be identical, but for Anthropic backends a Role::System message in messages serializes as a user turn — the system field ends up empty. Fix StructuredJudge::build_request to use instructions (as InstructionBlock), and update the tests in llm_class.rs and escalation.rs that were asserting the old messages-based shape.

[github-actions]

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[coderabbitai]

Walkthrough

The structured judge request now sends contract prompts through system instruction blocks. Conversation messages remain separate. Mock clients and request-shape tests now validate the updated protocol structure.

Changes

Structured judge request migration

Layer / File(s)	Summary
Build requests with instruction blocks crates/libsy/src/algorithms/util/llm_judge.rs	StructuredJudge::build_request places the contract prompt in a system InstructionBlock. Classifier-generated messages remain in messages.
Update structured request assertions crates/libsy/src/algorithms/llm_class.rs, crates/libsy/src/algorithms/util/escalation.rs	Tests extract prompts from instruction blocks and assert separate system instructions and conversation messages.

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

Poem

A rabbit sees prompts hop to their place,
System instructions lead the race.
Messages follow in tidy rows,
Tests now check the path it shows.
Hop, hop—structured requests compose!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: moving the judge system prompt from messages to instructions.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

• Create stacked PR
• Commit on current branch

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[ryan-lempka]

LGTM