fix: resolve session deletion hierarchy corruption, auto-title protocol errors, and test suite failures

[AyushDubey23]

Summary

Fixes three critical bugs affecting session management reliability, auto-titling stability, and test suite execution.

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Changes

1. Session Deletion Hierarchy Corruption (app/api/sessions/[id]/route.ts)

When deleting a parent session, child sessions should be re-parented to the grandparent. This failed silently on Windows because parentSession header paths were compared with raw string equality — mismatched slash directions (\ vs /) and drive letter casing caused the lookup to miss every child, leaving them with dangling parent pointers and corrupting the sidebar session tree.

Fix: Normalize paths with normalizeSlashes() and use case-insensitive comparison before rewriting child headers.

2. Auto-Title Generation LLM Protocol Error (lib/session-title.ts)

When a session ended mid-tool-call (e.g. interrupted bash execution), generateSessionTitle() passed the raw message history — including assistant messages with unfulfilled toolCall blocks — directly to the title-generation model. This violated the LLM turn protocol (tool calls must be followed by tool results before a user message), causing 400 Bad Request errors from every major provider.

Fix: Added sanitizeTitleMessages() to strip incomplete tool call blocks from assistant messages before forwarding to the title agent.

3. Unit Test Suite Module Loading Failures (lib/*.test.mjs)

52 out of 89 unit tests failed with ERR_UNKNOWN_FILE_EXTENSION because test files used native import("./*.ts") which Node's ESM loader rejects for TypeScript files. Additionally, two symlink-dependent tests crashed with EPERM on non-admin Windows.

Fix:

• Updated all 15 affected test files to use jiti.import() for TypeScript module loading (consistent with the pattern already used by session-reader.test.mjs).
• Added EPERM graceful handling for symlink tests on Windows (bash-output.test.mjs, file-upload.test.mjs, file-dirent.test.mjs).
• Fixed platform-dependent path assertion in bash-output.test.mjs.

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Verification

• TypeScript: tsc --noEmit — 0 errors
• Unit Tests: node --test lib/*.test.mjs — 95/95 passed (100%)