feat(SEM-53): Implement layered query resolution with deduplication

[Kadajett]

Summary

• Implements layered query resolution for the LayeredIndex with proper layer precedence (AI > Working > Branch > Base)
• Adds LayeredSearchOptions builder for configuring search (filters, limit, case sensitivity)
• Adds LayeredSearchResult type containing symbol info with layer metadata
• Implements search_symbols() that merges and deduplicates results across all layers
• Implements get_file_symbols() that resolves paths through file moves and returns deduplicated symbols
• Higher layers shadow lower layers; deleted markers in any higher layer exclude the symbol
• Fixes grammar bug in UpdateStrategy::description() (singular "file" vs plural "files")

Test plan

• 232 tests passing (31 new tests added)
• test_ai_layer_shadows_base_in_search - AI layer version returned, not base
• test_deleted_marker_stops_search - Deleted symbols excluded from results
• test_file_move_resolves_path_in_get_file_symbols - Old paths resolve through moves
• test_search_merges_all_layers - Symbols from all 4 layers found
• test_deduplication_across_layers - Same hash deduplicated to highest layer
• test_layer_ordering_correct - Results ordered AI → Working → Branch → Base
• Additional tests: case sensitivity, filters, limits, chained moves, resurrection after deletion

Closes SEM-53

-- Details

Adds search and file symbol resolution across layer stack with proper precedence (AI > Working > Branch > Base). Higher layers shadow lower layers, and deleted markers stop search.

New types:

• LayeredSearchOptions: Builder-pattern search configuration
• LayeredSearchResult: Search result with layer info

New methods on LayeredIndex:

• search_symbols(query, opts): Search across all layers
• get_file_symbols(path): Get symbols for a file with move resolution
• resolve_symbol_with_layer(hash): Resolve symbol with layer info
• total_active_symbols(): Count unique active symbols

Features:

• Layer precedence with deduplication
• Deleted marker handling
• File move resolution through layer chain
• Case-insensitive search (default)
• Filters: kind, risk, limit, layers

Includes 31 new tests (6 TDD required + 25 comprehensive). Also fixes singular/plural grammar in UpdateStrategy::description().

[linear]

SEM-53 Layered Query Resolution

Overview

Implement query resolution across layer stack.

Resolution Algorithm

fn get_symbol(hash: &str, layers: &[Layer]) -> Option<Symbol> {
    for layer in [AI, Working, Branch, Base] {
        if layer.deleted.contains(hash) {
            return None;  // Explicitly deleted
        }
        if let Some(s) = layer.symbols.get(hash) {
            return Some(s);  // Found in overlay
        }
    }
    None  // Not found anywhere
}

Check layers top-down (AI → Working → Branch → Base).
First match wins. Deleted markers stop search.

TDD Requirements

#[test] fn test_ai_layer_shadows_base() { }
#[test] fn test_deleted_marker_stops_search() { }
#[test] fn test_file_move_resolves_path() { }
#[test] fn test_search_merges_all_layers() { }
#[test] fn test_deduplication_across_layers() { }
#[test] fn test_layer_ordering_correct() { }

Deliverables

• resolve_symbol(hash: &str) -> Option<Symbol> with layer precedence
• search_symbols(query: &str, opts: SearchOptions) -> Vec<SearchResult>
  • Merges results from all layers
  • Deduplicates (higher layer wins)
  • Respects deleted markers
• get_file_symbols(path: &Path) -> Vec<Symbol>
  • Resolves path through move history
• resolve_file_path(path: &Path) -> Option<PathBuf>
  • Traces file through renames across layers

Acceptance Criteria

• Symbol in AI layer shadows same symbol in lower layers
• Deleted marker in Working layer hides symbol from Base
• File moves resolve correctly through all layers
• Search merges and deduplicates across layers

[Copilot]

Pull request overview

This pull request implements layered query resolution for the LayeredIndex with proper layer precedence (AI > Working > Branch > Base), enabling efficient symbol search and retrieval across the layer stack with deduplication.

Key Changes

• Adds LayeredSearchOptions builder for configuring symbol searches with filters (kind, risk, limit, layers) and case sensitivity
• Implements search_symbols() method that merges and deduplicates results across all layers, respecting deletion markers
• Adds get_file_symbols() with file move resolution through the layer chain
• Includes comprehensive test coverage (31 new tests) covering TDD requirements and edge cases
• Fixes grammar bug in UpdateStrategy::description() (singular vs plural "file"/"files")

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/overlay.rs	Implements core layered query resolution with LayeredSearchOptions, LayeredSearchResult, and search methods (search_symbols, get_file_symbols, resolve_symbol_with_layer, total_active_symbols). Includes 31 comprehensive tests.
src/lib.rs	Re-exports new public types LayeredSearchOptions and LayeredSearchResult
src/drift.rs	Fixes test for UpdateStrategy::description() to properly verify singular/plural grammar

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