fix: reduce false-positive merge suggestions from single-word display names (CM-1137)

[skwowet]

Summary

Follow-up to #4115.

The first production run surfaced:

• ~21k single-word first-name collisions (Alex, David, Scott, etc.) scoring 0.9 with no corroborating signal.
• ~259 placeholder-name pairs ([[Unknown]] [Not Provided], Deleted User) incorrectly treated as valid merge candidates.

Changes

• Single-word display names now require at least one corroborating signal (location, org, timezone, or local-part).
• Only full names (i.e. names containing a space) are treated as high-confidence on their own.
• Added [[Unknown]] [Not Provided] and Deleted User to the placeholder-name blocklist.

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Note

Medium Risk
Adjusts merge-similarity scoring logic used to propose member merges; mistakes could reduce recall or still allow some false positives, but changes are localized to heuristics.

Overview
Reduces false-positive merge suggestions when members share the same displayName.

Exact displayName matches now return low confidence for OS/placeholder names via isOsReservedName, and treat single-word names as requiring corroborating signals by starting decideMemberSimilarityUsingAdditionalChecks at HIGH_CONFIDENCE_SCORE (only multi-word “full names” remain high-confidence on display name alone).

Expands the OS_RESERVED_NAMES blocklist in utils.ts to include [[Unknown]] [Not Provided] and Deleted User.

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[Copilot]

Pull request overview

This PR tightens member merge similarity scoring to reduce false positives from ambiguous single-word display names and known placeholder names.

Changes:

• Adds [[Unknown]] [Not Provided] and Deleted User to the non-identity name blocklist.
• Changes exact display-name scoring so single-word names require corroborating signals, while multi-word names remain high-confidence.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
services/apps/merge_suggestions_worker/src/utils.ts	Expands reserved/non-identity display name handling.
services/apps/merge_suggestions_worker/src/memberSimilarityCalculator.ts	Adjusts exact display-name scoring for single-word vs full-name cases.

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