feat(openai): configure trusted agent session header

[i386]

Problem

The OpenAI frontend supports a configurable trusted agent-session header, but the default router ignored that configuration. A Mesh process launched with a trusted upstream session-header setting therefore treated every request as stateless.

Change

OpenAiFrontendConfig::default() now reads the optional MESH_AGENT_SESSION_HEADER environment variable and applies it as the trusted header. Existing callers remain unchanged when the variable is absent, and explicit with_agent_session_header configuration still takes precedence.

Invalid or non-UTF-8 values emit a startup warning and are ignored rather than silently looking like a valid configuration. Parser coverage covers valid and invalid names.

This keeps the boundary generic: Mesh does not hard-code Cacheline or a benchmark-specific header name.

Validation

• cargo fmt --all -- --check
• cargo test -p openai-frontend --lib (153 passed)
• cargo clippy -p openai-frontend --lib --all-targets -- -D warnings

[coderabbitai]

📝 Walkthrough

Walkthrough

The OpenAI frontend reads MESH_AGENT_SESSION_HEADER during default configuration. Valid values configure the trusted agent-session header. Missing or invalid values disable header-derived session identity. The README documents the environment variable.

Changes

Trusted Agent Session Header

Layer / File(s)	Summary
Environment-based header configuration crates/openai-frontend/src/router.rs, crates/openai-frontend/README.md	The frontend parses MESH_AGENT_SESSION_HEADER as an HTTP header name, applies valid values to OpenAiFrontendConfig::default, tests valid and invalid names, and documents the variable.

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

Possibly related PRs

• Mesh-LLM/mesh-llm#1152: This PR extends the same trusted agent-session header configuration in crates/openai-frontend/src/router.rs.

Suggested reviewers: ndizazzo

🚥 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: configurable trusted agent session header support in the OpenAI frontend.

✨ 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 agent/configurable-agent-session-header

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[github-actions]

This pull request is currently a draft. Reviews will not take place until the PR is marked as ready for review.

[coderabbitai]

🧹 Nitpick comments (1)

crates/openai-frontend/src/router.rs (1)

50-56: 🩺 Stability & Availability | 🔵 Trivial | ⚡ Quick win

Make invalid header configuration observable.

configured_agent_session_header returns None for both an unset variable and an invalid value. A configuration typo therefore silently disables AgentSessionIdentity extraction. Emit a startup warning or make invalid configuration fail during construction. Add coverage for absent, invalid, and valid values.

🤖 Prompt for 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.

In `@crates/openai-frontend/src/router.rs` around lines 50 - 56, Update
configured_agent_session_header to distinguish an unset
MESH_AGENT_SESSION_HEADER from an invalid header value, emitting a startup
warning or failing during router construction for invalid configuration while
preserving None for absent configuration. Add coverage covering absent, invalid,
and valid environment values.

🤖 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.

Nitpick comments:
In `@crates/openai-frontend/src/router.rs`:
- Around line 50-56: Update configured_agent_session_header to distinguish an
unset MESH_AGENT_SESSION_HEADER from an invalid header value, emitting a startup
warning or failing during router construction for invalid configuration while
preserving None for absent configuration. Add coverage covering absent, invalid,
and valid environment values.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 3554fa11-b05b-480f-a518-0cc50fa317d3

📥 Commits

Reviewing files that changed from the base of the PR and between 915e691 and 1d7ce1d.

📒 Files selected for processing (2)

• crates/openai-frontend/README.md
• crates/openai-frontend/src/router.rs

[i386]

Addressed the review nit in 7330de1. MESH_AGENT_SESSION_HEADER now distinguishes unset, non-UTF-8, and invalid header values; invalid configuration emits a startup warning instead of silently disabling session identity. Added parser coverage for valid and invalid names. Validation: cargo fmt --all -- --check, cargo test -p openai-frontend --lib (153 passed), and clippy with -D warnings.

[ndizazzo]

Ah perfect, this shoukd help us let models dispatch from codex to other CLI tools