feat(ext): expose the detected session ID to request rewriters

[SantiagoDePolonia]

Summary

Adds SessionID to ext.Input. Session detection (SessionCapture) already runs before RequestRewriteMiddleware, so the user-path-scoped session ID is in the request context when rewriters fire — this just surfaces it.

Motivation: lets a rewriter keep per-conversation decisions stable across messages, e.g. GoModel Pro's content-aware tier router pinning its easy/hard model choice to the session instead of re-deciding (and potentially flip-flopping) on every message.

Stacked on #611 (base: feat/ext-route-selector); rebase to main if it lands first.

Tests

TestRequestRewriteMiddlewareExposesSessionID — stamps a session via ExtraMiddleware (which runs before rewriters, standing in for the detector) and asserts the rewriter observes it.

🤖 Generated with Claude Code

Summary by CodeRabbit

• New Features
  • Request rewriters can now access the detected client session ID via the rewrite input, enabling consistent decisions across a conversation.
• Bug Fixes
  • Session information is now correctly carried through the request-rewriting flow so it’s available to rewriters as expected.
• Tests
  • Added coverage to verify request rewriters receive the expected session ID during rewriting.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: a23252a3-756a-4e09-b03c-f9a79184d4ac

📥 Commits

Reviewing files that changed from the base of the PR and between 1a3bd5b and 5a91572.

📒 Files selected for processing (3)

• ext/ext.go
• internal/server/request_rewrite.go
• internal/server/request_rewrite_test.go

📝 Walkthrough

Walkthrough

ext.Input now exposes the detected session ID to request rewriters. RequestRewriteMiddleware populates it from request context, and a test verifies propagation through session stamping and rewriting.

Changes

Session ID propagation

Layer / File(s)	Summary
Session ID input and middleware propagation ext/ext.go, internal/server/request_rewrite.go, internal/server/request_rewrite_test.go	ext.Input includes a path-scoped SessionID; request rewriting copies it from context, and middleware coverage verifies that rewriters receive the stamped value.

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

Poem

A rabbit twitched its nose with glee,
“A session tag now hops along!”
Through context fields and rewrite paths,
The rewriter finds where it belongs.
“sess-42!” we cheer in song.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly states the main change: exposing detected session IDs to request rewriters.
Description check	✅ Passed	It covers what changed, why, and testing, though it uses Summary/Tests instead of the template's Description section.
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 unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/ext-session-id

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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 `@internal/server/request_rewrite_test.go`:
- Around line 122-154: Convert TestRequestRewriteMiddlewareExposesSessionID into
a table-driven test covering both a populated session ID and an absent session
ID. For each case, configure the session-stamping middleware accordingly,
execute the request, and assert the rewriter observes the expected session
value, including an empty default when no session is present.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

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

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: ef829019-e33f-432e-920d-8082be09d54a

📥 Commits

Reviewing files that changed from the base of the PR and between c31d624 and 3d71ff7.

📒 Files selected for processing (3)

• ext/ext.go
• internal/server/request_rewrite.go
• internal/server/request_rewrite_test.go

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The session-capture middleware runs before request rewriting and stores the identifier in the same request context from which the new field is populated; existing repository construction of the extended input uses keyed fields.

Files Needing Attention: No files need attention.

T-Rex Logs

What T-Rex did

• The TestRequestRewriteMiddlewareExposesSessionID test was executed and passed with a 200 status for POST /v1/chat/completions.
• The server package gomodel/internal/server reported an ok result in about 0.007 seconds.
• A log artifact captures the test run evidence for review and verification.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "feat(ext): expose the detected session I..." | Re-trigger Greptile}

[SantiagoDePolonia]

Converted the session-propagation test to table-driven cases (detected session propagates / no session yields empty) in 5a91572, and rebased on the latest #611.