Validate HTTP/2 header casing and lowercase default user-agent

[vincenthawke]

Added HTTP/2 header casing validation to the SessionClient constructor. When forceHttp1 is false, both defaultHeaders and connectHeaders are checked, and an error is thrown if any header name is not lowercase.

Renamed the user-agent header in DEFAULT_OPTIONS.defaultHeaders to lowercase.

No header casing validation is performed when forceHttp1 is true, since HTTP/1.1 does not require lowercase header names

Summary by CodeRabbit

• Bug Fixes
  • Standardized the default User-Agent header key to lowercase.
  • Added validation for default and CONNECT header names when HTTP/1 is not forced, preventing invalid non-lowercase headers.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 80fe857a-f273-4672-9669-2bab382e324e

📥 Commits

Reviewing files that changed from the base of the PR and between 400d5cc and ea0c4d9.

📒 Files selected for processing (1)

• src/index.ts

📝 Walkthrough

Walkthrough

The client now uses a lowercase user-agent header by default. SessionClient rejects non-lowercase default and CONNECT headers when HTTP/1 is not forced.

Changes

HTTP Header Validation

Layer / File(s)	Summary
Default headers and casing validation src/index.ts	The default User-Agent header is now user-agent. SessionClient combines default and CONNECT header names and rejects non-lowercase names unless forceHttp1 is enabled.

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

Suggested reviewers: claude

🚥 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 clearly summarizes both main changes: HTTP/2 header casing validation and the lowercase default user-agent header.
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.

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[coderabbitai]

Actionable comments posted: 2

🤖 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/index.ts`:
- Around line 565-573: Update the header validation condition near allHeaders so
validation runs whenever options.forceHttp1 is not true, including when it is
omitted, while still skipping it for explicit true. Add tests covering omitted
forceHttp1 and uppercase defaultHeaders/connectHeaders, explicit false, and
explicit true.
- Line 511: Update the README defaultHeaders example to use the lowercase
`user-agent` header key instead of `User-Agent`, keeping the documented
`forceHttp1: false` configuration unchanged.

🪄 Autofix

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: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 9181c361-454d-4d58-8a85-bb52b139a136

📥 Commits

Reviewing files that changed from the base of the PR and between ca9e54c and 400d5cc.

📒 Files selected for processing (1)

• src/index.ts