fix(agent): compare broker client executables by file identity

[Vladyslav Nikonov (vnikonov-devolutions)]

The package broker authenticated pipe clients by comparing executable path strings using a lossy, ASCII-case-insensitive comparison. This was fragile for a security-relevant identity check, as it could be tripped up by Unicode casing rules, invalid UTF-8, and other path representation edge cases.

The broker now opens both executables and compares their file identity directly (volume serial number + 128-bit file ID via GetFileInformationByHandleEx/FILE_ID_INFO), which is immune to these edge cases.

Issue: DGW-419

[github-actions]

Let maintainers know that an action is required on their side

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[Vladyslav Nikonov (vnikonov-devolutions)]

Implementation notes:

• Replaces the canonicalize + to_string_lossy().eq_ignore_ascii_case() path comparison with a handle-based identity check, addressing feat(agent): implement package broker #1847 (comment) and feat(agent): implement package broker #1847 (comment).
• file_id() opens the file with FILE_READ_ATTRIBUTES access and full sharing, then queries FileIdInfo via GetFileInformationByHandleEx. Identity = volume serial number + 128-bit file ID, robust against Unicode casing, invalid UTF-8, 8.3 short names, symlinks/junctions, and subst drives.
• The redundant canonicalize_for_comparison helper and same_windows_path are removed.
• Tests: two new unit tests verify that different path spellings of the same file (casing, redundant . component) yield the same identity, and that distinct files yield different identities.

[Copilot]

Pull request overview

Replaces fragile executable path-string comparison with Windows file identity checks for broker client authentication.

Changes:

• Compares volume serial numbers and 128-bit file IDs.
• Adds tests for equivalent paths and distinct files.

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[Benoît Cortier (CBenoit)]

LGTM!