[cakeni]

Summary

Allow [[sub-config]]'s matches key to accept either a single glob string or a non-empty list of glob strings. A listed sub-config applies when any entry matches, while existing single-string configurations retain their current behavior and precedence.

The change also updates migration code and configuration documentation, and adds coverage for single values, multiple values, and rejection of an empty list.

Fixes #4462

Test Plan

• python test.py --no-test --no-tensor-shapes --no-conformance --no-jsonschema (formatting passed; local lint compilation is blocked by the installed MinGW headers while building mimalloc)
• GitHub Actions on the fork branch is in progress with no failures reported at PR creation time

[meta-codesync]

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[github-actions]

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Thank you for your contributions!

[cakeni]

Still working on this; keeping it active for review.

[stroxler]

Hi @cakeni - sorry for the slow turnaround on this.

Unfortunately, this PR is tied to a stale diff internally, which makes it hard for me to review and merge it. Would you mind closing this PR and opening a fresh one? Then you can assign it to me - I should be able to turn around review much faster.

While you're at it, could you make a couple of minor adjustments? An initial AI review flagged two potential issues:

1. The JSON schema rejects the new list syntax.
   [schemas/pyrefly.json:376–378](https://github.com/meta/pyrefly/blob/9beaefd178062f7e7341a761c6c26b7264caae43/schemas/pyrefly.json#L376-L378) still requires "type": "string". I confirmed the documented matches = ["src/first.py", "tests/second.py"] example fails validation for both pyrefly.toml and pyproject.toml.
   Fix: accept a string or an array of strings with minItems: 1, and add positive-list and empty-list schema tests.

2. Invalid-glob diagnostics regress, including for existing scalar configs.
   [config.rs:135–142](https://github.com/meta/pyrefly/blob/9beaefd178062f7e7341a761c6c26b7264caae43/crates/pyrefly_config/src/config.rs#L135-L142) uses an untagged enum that discards the underlying Glob error. For matches = "src/[a", the useful message identifying the malformed pattern becomes data did not match any variant of untagged enum OneOrMany. A bad list entry produces the same generic error.
   Fix: use a string-or-sequence serde visitor that propagates glob errors directly, with regression tests for malformed scalar and list entries.

[stroxler]

Once again just to make sure it doesn't get lost: to help me turn this around, could you not only address those concerns, but close this PR and open a fresh one, assigned to me?