feat: preserve diff context during LSP navigation

docs/architecture.md

@@ -21,7 +21,7 @@ One editor crate; the workspace also includes its patched Crossterm dependency.
 - `plugin`: owns generic document snapshots/events, zero-based grapheme positions, diagnostics, frontend-independent semantic token kinds/modifiers and completion edit/item DTOs, and versioned asynchronous update contracts. Semantic token and completion updates are native-only, not part of the Ruby wire protocol; it has no LSP protocol types.
 - `lsp`: owns opt-in native server workers, bounded framed JSON-RPC, synchronization/capability negotiation, settings, UTF-16/file-URI conversion, definition/hover results, completion decoding, and semantic token requests/legend decoding. Its private configuration resolver supplies presets without restricting language IDs.
 - `snippet`: owns bounded, frontend-independent template parsing and expansion into plain replacement text and byte-relative tabstops with per-occurrence ancestry. It never edits documents or owns input policy.
-- `session`: `EditorSession` owns the editor, native LSP, and Ruby hosts together. It loads configuration once, registers eligible plugins before installing shared bindings, tracks document open/change/save/close events, polls native and plugin results, validates versioned diagnostics/navigation/completion, and retires failed plugin ownership. Each tab with a comparison has a cancellable repository worker; inactive tabs keep their workers and receive tagged results without changing visible focus. Closed or superseded comparisons reject stale results. Diff focus suppresses asynchronous editing/navigation effects without retiring healthy plugins.
+- `session`: `EditorSession` owns the editor, native LSP, and Ruby hosts together. It loads configuration once, registers eligible plugins before installing shared bindings, tracks document open/change/save/close events, polls native and plugin results, validates versioned diagnostics/navigation/completion, and retires failed plugin ownership. Each tab with a comparison has a cancellable repository worker; inactive tabs keep their workers and receive tagged results without changing visible focus. Closed or superseded comparisons reject stale results. Focused diff text supports native LSP navigation, hover, and diagnostics; read-only buffers still reject asynchronous editing effects, and selectors/file lists are not document-action targets.
 - `tui`: translates terminal events to session input, renders read-only active-buffer state, keeps frontend-owned viewports and syntax caches by stable buffer ID or immutable diff snapshot/file identity, and advertises `text`, `styled_text`, and `diagnostics` capabilities. It maps semantic tokens and diagnostics to terminal styling and has no server/protocol logic or paste acceptance policy.
 - `ruby`: evaluates configuration and runs isolated plugin hosts. Protocol, deadlines, and process cleanup stay inside this module.
 - The executable selects paths and frontend capabilities, opens an editor session, and launches the TUI.
@@ -85,6 +85,8 @@ macOS uses fixed JXA/AppKit `NSPasteboardTypeString` access through `osascript`,
 
 The native module initializes each server, sends `initialization_options` as `initializationOptions`, answers `workspace/configuration` from `settings` (including dotted sections; missing sections return `null`), honors open/change/save capabilities, synchronizes in-memory text including hidden dirty buffers, and sends close events. Incremental servers receive whole-document range replacements. Process/pipe I/O and requests stay on bounded background workers; input and idle diagnostic redraw do not wait for server responses.
 
+Diff snapshots retain a separate immutable document identity, full source text, side-specific path (the old path for renamed Before), and UTF-16 positions. Native definition updates preserve their UTF-16 ranges until the editor resolves the target's actual snapshot, dirty buffer, disk text, or lazily loaded comparison file; generic plugin navigation remains grapheme-based. Target ranges overlapping actual changed rows route within the same comparison and reveal the exact selection, including an unchanged declaration above a changed body. Wholly unchanged/context/omitted targets and files outside its changes open an ordinary tab without changing the original comparison or view. Snapshot-URI targets keep their immutable identity. Freshness includes tab, pane, source buffer/revision/caret/mode, and comparison/side; deferred file-load navigation also checks its originating view before moving focus. Invalid targets fail before opening a tab. Completion remains restricted to writable Working After.
+
 Language configurations can own an ordered server stack. The first matching language wins extension overlap; all its matching servers receive document events, while the first handles hover/definition/completion. The Python preset uses ty then Ruff. LSP merges each worker's latest diagnostic snapshot in assignment order before emitting the unchanged core-owned update. Empty publications/retirement remove only their source; revision/path/root changes and close discard all contributions. Worker snapshots retain identity so queued pre-rename diagnostics cannot attach to a new path with the same text revision. Combined diagnostic message bytes remain bounded to 4 MiB; an overflowing publication retires its worker instead of discarding healthy sibling annotations. Workers are stored in config/root order, avoiding per-poll key cloning/sorting. Shutdown flushes the exit notification and waits for peer termination within the existing bounded grace period before process cleanup.
 
 Semantic tokens belong only to the first assigned server. Initialization advertises standard token types/modifiers, relative encoding, full/range requests, and server refresh support; deltas, overlapping/multiline tokens, and dynamic registration are not advertised. Each buffer has at most one request in flight; changes/refreshes coalesce into the latest snapshot. Full requests are preferred, with whole-document range fallback. A linear UTF-16 decoder validates raw coordinates and legend indices before outward grapheme rounding; overlong ends truncate at EOL, unknown types and invisible spans fall back to syntax. Both wire frames and decoded spans are bounded to 4 MiB. Snapshot identity rejects stale/renamed/closed replies before decoding. Invalid semantic replies clear the overlay and report an error without retiring diagnostics/navigation; primary retirement clears its overlays, and sibling retirement leaves them intact.