fix(ui): ensure session deletion properly clears backend and cache

[keval718]

Problem

In release-1.8.0, the session deletion logic was failing to properly purge data from both the UI and backend, manifesting in two critical ways:

Context Persistence: Deleting the "Default Session" cleared the chat UI, but the LLM retained memory of previous messages
Data Leakage/Reuse: Deleting a numbered session (e.g., "New Session 0") and creating a new one caused the system to reuse the old session's data, with messages from the deleted session immediately reappearing

Root Cause
The system was performing "shallow deletions" that only affected the sidebar UI. The backend deletion API was never called for numbered sessions due to a conditional check that required the session to be in the dbSessions list first.

Testing
✅ Verified numbered sessions now call backend API on deletion
✅ Confirmed Message Logs shows empty state after deletion
✅ Tested session recreation doesn't reuse old data
✅ Verified no context persistence after deletion

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[github-actions]

Frontend Unit Test Coverage Report

Coverage Summary

Lines	Statements	Branches	Functions
	23.27% (8148/35009)	15.97% (4390/27476)	16.12% (1188/7367)

Unit Test Results

Tests	Skipped	Failures	Errors	Time
2653	0 💤	0 ❌	0 🔥	46.105s ⏱️

[codecov]

Codecov Report

❌ Patch coverage is 0% with 39 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release-1.8.0@73aad93). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...ollers/API/queries/messages/use-delete-sessions.ts	0.00%	21 Missing ⚠️
.../chat-view/chat-messages/hooks/use-chat-history.ts	0.00%	9 Missing ⚠️
...ygroundComponent/chat-view/utils/session-filter.ts	0.00%	6 Missing ⚠️
...at-view/chat-header/hooks/use-edit-session-info.ts	0.00%	2 Missing ⚠️
...end/src/modals/IOModal/components/session-view.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##             release-1.8.0   #12043   +/-   ##
================================================
  Coverage                 ?   37.16%           
================================================
  Files                    ?     1592           
  Lines                    ?    78102           
  Branches                 ?    11842           
================================================
  Hits                     ?    29023           
  Misses                   ?    47425           
  Partials                 ?     1654           

Flag	Coverage Δ
backend	57.28% <ø> (?)
frontend	20.83% <0.00%> (?)
lfx	41.50% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...hat-view/chat-header/hooks/use-get-add-sessions.ts	0.00% <ø> (ø)
...end/src/modals/IOModal/components/session-view.tsx	0.00% <0.00%> (ø)
...at-view/chat-header/hooks/use-edit-session-info.ts	0.00% <0.00%> (ø)
...ygroundComponent/chat-view/utils/session-filter.ts	0.00% <0.00%> (ø)
.../chat-view/chat-messages/hooks/use-chat-history.ts	0.00% <0.00%> (ø)
...ollers/API/queries/messages/use-delete-sessions.ts	0.00% <0.00%> (ø)

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[Cristhianzl]

🟠 NEEDS CHANGES

Must fix (blockers):

1. DRY violation — Extract session filtering logic into a shared isMessageForSession(msg, flowId, session) helper used by both the useEffect initializer and the useMemo display filter
2. any types — Replace 6+ any usages in use-delete-sessions.ts with proper types. The original code used useMutationFunctionType — either keep using it or define DeleteSessionResponse and Error types
3. Unnecessary cast — Remove as unknown as DeleteSessionParams — variables is already typed correctly

Should fix:
4. Tests — Add regression tests for the data leakage fix, at minimum covering: (a) delete removes cache, (b) new session after delete starts clean, (c) session filtering correctness
5. sessionStorage double-write — Either remove the explicit sessionStorage cleanup in removeLocalSession (since the useEffect on line 67-77 already handles it), or add a comment explaining why both are needed (race condition?)

Nice to have:
6. Simplify ExtendedMessageProperties — the base Message type has [key: string]: unknown so the extension adds no type safety
7. Change comments from WHAT to WHY
8. Consider centralizing query key factories to avoid tight coupling in predicate-based cache removal

[keval718]

🟠 NEEDS CHANGES

Must fix (blockers):

1. DRY violation — Extract session filtering logic into a shared isMessageForSession(msg, flowId, session) helper used by both the useEffect initializer and the useMemo display filter
2. any types — Replace 6+ any usages in use-delete-sessions.ts with proper types. The original code used useMutationFunctionType — either keep using it or define DeleteSessionResponse and Error types
3. Unnecessary cast — Remove as unknown as DeleteSessionParams — variables is already typed correctly

Should fix: 4. Tests — Add regression tests for the data leakage fix, at minimum covering: (a) delete removes cache, (b) new session after delete starts clean, (c) session filtering correctness 5. sessionStorage double-write — Either remove the explicit sessionStorage cleanup in removeLocalSession (since the useEffect on line 67-77 already handles it), or add a comment explaining why both are needed (race condition?)

Nice to have: 6. Simplify ExtendedMessageProperties — the base Message type has [key: string]: unknown so the extension adds no type safety 7. Change comments from WHAT to WHY 8. Consider centralizing query key factories to avoid tight coupling in predicate-based cache removal

Fixed. Thanks