[Bug] Regression bug for shift key using Synergy

Describe the bug:
As people report here https://github.com/rime/squirrel/issues/1026 , when using squirrel on Mac remoting from Synergy, pressing shift key will show the "a" character and that also make the character selection screen show. Version 0.16.2 do not have this problem.

Expected behavior:
Shift key should be only showing shift key, not "a"

Actual behavior:
Pressing shift key using Synergy remoting into Mac will show the "a" character.

Environment

• OS version: MacOS 26.2
• Squirrel version: 1.0.3
• Schema: (If you are using a custom schema, and think it might be related to the schema, please provide a link)
• Using Lua: (what Lua script do you use?)
• Related to other apps: (Synergy)

Things you've tried

• [X ] I tried a built-in schema (like luna pinyin), but the bug persists
• [X ] I found the exact setting that produced this bug: (as decribed)
• [X ] This bug is new in this version (I believe it affect all version after 0.16.2
• I think the cause might be: (your thoughts)
• I don't find a similar report in Issues (including closed Issues)

Start by reproducing the issue with Synergy remoting into macOS, using Squirrel 1.0.3 and the built-in Luna Pinyin schema. Compare the behavior with version 0.16.2 and trace how a remote Shift key is interpreted. Done means Shift no longer emits “a” or opens the character selection screen.