fix(hooks): isolate initialization by host session

[escott-]

Starting or resuming a second session in the same checkout could reset the shared initialization gate and block an already initialized Claude/Codex session with “First call required.” Initialization is now tracked by the top-level host session ID in a separate, locked state file with atomic replacement. Replayed session-start events preserve successful setup, while each fresh session still requires initialization.

Record completion after a successful init or context result and include quick-start context/session grounding in the managed post-tool matcher. File-indexing disablement continues to allow initialization receipts. Existing hook settings are preserved.

Validation: 12 focused Rust tests passed, including parallel session isolation, replay, failed results, aliases, concurrent writers and matcher preservation. cargo fmt --all --check and cargo clippy --locked -p mcp-server --lib --tests -- -D warnings passed. The patched macOS helper is installed locally; real MCP calls across separate execution cells pass without repeated initialization. Installed-helper regression probes confirm fresh-session denial, failed-init denial, successful context quick-start and same-folder session isolation.

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