fix(engine): align predicted-gate collision risk with live gate

[RealDiligent]

Summary

• Removes the extra issue.linkedPrs.length > 1 clause from predicted-gate buildCollisionReport risk so it matches the canonical live-gate twin in engine.ts.
• Adds a regression test: a single freshly-linked PR stays medium risk even when the issue's stale linkedPrs field lists multiple PRs.

Closes #6629

Test plan

• New fix(engine): predicted-gate-engine's buildCollisionReport risk check has an extra issue.linkedPrs clause its live-gate twin doesn't #6629 collision-parity regression passes
• Existing predicted-gate collision parity suite still green
• codecov/patch green

Made with Cursor

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

[JSONbored]

Above 2 PR cap.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.65%. Comparing base (5a2db4c) to head (ffefca4).
⚠️ Report is 18 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6665   +/-   ##
=======================================
  Coverage   93.64%   93.65%           
=======================================
  Files         680      681    +1     
  Lines       68026    68088   +62     
  Branches    18671    18692   +21     
=======================================
+ Hits        63704    63766   +62     
  Misses       3347     3347           
  Partials      975      975           

Flag	Coverage Δ
shard-1	43.99% <0.00%> (+0.05%)	⬆️
shard-2	36.87% <0.00%> (-0.13%)	⬇️
shard-3	32.42% <100.00%> (+0.01%)	⬆️
shard-4	34.57% <100.00%> (+0.80%)	⬆️
shard-5	30.93% <100.00%> (-0.69%)	⬇️
shard-6	45.69% <100.00%> (-0.10%)	⬇️

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Files with missing lines	Coverage Δ
...opover-engine/src/signals/predicted-gate-engine.ts	100.00% <100.00%> (ø)