fix(gmail): match message header names case-insensitively (#642)

[shigechika]

Summary

Fixes #642.

parse_message_headers matched header field names with exact case:

match name {
    "From" => ...
    "Cc" => ...
    ...
}

Gmail preserves the sender's original header casing, so a message whose Cc
header arrives as "CC" (very common from Exchange/Outlook) — or "from"
lowercase from some MTAs — falls through the match and is silently dropped.
In practice this drops all CC recipients from gws gmail +reply-all.

Per RFC 5322 §1.2.2 header field names are case-insensitive. The sibling get_part_header already uses eq_ignore_ascii_case, so this just brings parse_message_headers in line.

Fix

Normalize the name to lowercase before matching:

match name.to_ascii_lowercase().as_str() {
    "from" => ...
    "cc" => ...
    ...
}

(The previous "Message-ID" | "Message-Id" arm collapses to a single
"message-id".)

Test

Adds test_parse_message_headers_case_insensitive, covering mixed-case
FROM / to / CC / Reply-TO / subject / MESSAGE-ID / References.

cargo build clean; cargo test helpers::gmail green (235 passed).

🤖 Generated with Claude Code

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🦋 Changeset detected

Latest commit: 78e0ae1

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@googleworkspace/cli	Patch

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where Gmail message headers were being silently ignored if their casing did not match the hardcoded strings in the parser. By normalizing header names to lowercase, the system now correctly handles various casing formats often produced by different MTAs and email clients like Outlook, ensuring that critical fields like CC are preserved during operations such as reply-all.

Highlights

• Case-Insensitive Header Matching: Updated the parse_message_headers function to normalize header names to lowercase before matching, ensuring compliance with RFC 5322 and preventing headers from being silently dropped due to casing variations.
• Regression Testing: Added a new test case test_parse_message_headers_case_insensitive to verify that mixed-case header names are correctly parsed.

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[gemini-code-assist]

Code Review

This pull request fixes an issue where Gmail message headers were matched case-sensitively, causing headers with non-canonical casing (like "CC" or lowercase "from") to be silently dropped. The matching logic in parse_message_headers has been updated to normalize header names to lowercase before matching, and a corresponding unit test has been added to verify case-insensitive parsing. There are no review comments, so I have no feedback to provide.

[lucaspretti]

Hey @shigechika, thanks for picking this up. I submitted the same fix in #846 (a re-submission of #841), but the stale bot closed both before a maintainer could take a look.

Since the diff here is essentially identical, two small things from my version might be worth folding in:

• a regression test (test_parse_original_message_case_insensitive_headers) that feeds Exchange-style casing (FROM, TO, CC, cc, message-id) and asserts no recipient or the message id gets dropped;
• the old "Message-ID" | "Message-Id" arm collapsed into a single "message-id" case.

No ownership concerns on my end, just flagging so whichever PR lands keeps the test coverage. Glad to see this getting fixed either way.

[shigechika]

Thanks @lucaspretti — sorry the stale bot got both of yours. Good news: both points you raised are already covered here:

• the old "Message-ID" | "Message-Id" arm is collapsed into a single "message-id" case;
• test_parse_message_headers_case_insensitive feeds mixed Exchange-style casing (FROM/to/CC/Reply-TO/MESSAGE-ID/References) and asserts none of them are dropped.

Genuinely happy for whichever PR lands — the important thing is that #642 gets fixed. Thanks for flagging the test coverage either way.