Motivation

• Avoid building one giant Vec<Action> up front when indexing large trees to reduce peak memory usage and startup latency.
• Allow the UI and main startup/reload flows to receive and merge indexed actions progressively instead of waiting for a full scan to finish.
• Protect the process from unbounded memory growth and duplicate entries by adding canonical-path deduplication and a configurable max item cap.

Description

• Introduced IndexOptions and IndexBatchIter and a new API index_paths_batched(paths, options) that yields anyhow::Result<Vec<Action>> batches for streaming consumption. A compatibility helper index_paths exhausts the iterator for callers that need a Vec<Action>.
• Implemented canonical path deduplication using HashSet<PathBuf> and enforced a max_items cap while iterating; defaults are provided via IndexOptions::default() and helper IndexOptions::with_max_items(...).
• Updated startup indexing in src/main.rs to consume batches from index_paths_batched with IndexOptions::with_max_items(settings.max_indexed_items) and merge batches into actions_vec progressively.
• Updated action reload handling in src/gui/mod.rs to iterate batches from index_paths_batched, extend acts per-batch, and refresh self.actions, update_action_cache() and search() progressively as batches arrive, while still finalizing state at the end of the reload.
• Added Settings.max_indexed_items: Option<usize> and preserved it in SettingsEditor::to_settings so users can control the indexing cap via settings.
• Added tests in tests/indexer.rs to verify canonicalized output, deduplication across duplicate roots, batch sizing and honoring max_items.

Testing

• Ran cargo fmt which completed successfully.
• Added unit tests under tests/indexer.rs covering recursive indexing, canonicalized/display paths, batching, dedupe and max_items behavior (new tests included in the commit).
• Attempted to run cargo test tests::indexer -- --nocapture and cargo test --test indexer --no-default-features, but the local build was blocked by a missing system dependency required by alsa-sys (missing alsa.pc / pkg-config), so the test run failed to complete in this environment.

Codex Task