chore: break up EditorView.swift (5,436 lines)

[dep]

Context

Follow-up to #237 (AppState god-object refactor). EditorView.swift is the single largest file in the macOS app at 5,436 lines and contains at least 17 top-level types. Much of its size is not the SwiftUI view itself but a collection of AppKit classes, NSViewRepresentables, helper DTOs, and a ~410-line markdown styling engine that all happen to live in the same file.

Goal

Split EditorView.swift into focused, single-purpose files so that:

1. The actual EditorView SwiftUI struct is <500 lines and reads like a view, not a framework.
2. Markdown styling, wiki-link insertion, inline embeds, code-block buttons, and git history each live in their own testable unit.
3. The NSTextView subclass (LinkAwareTextView, ~1,400 lines on its own) is split by responsibility.
4. We can write unit tests against the styling engine without instantiating SwiftUI.

Non-goals: behavior changes, visual changes, or rewriting the regex-based styling. This is pure file-level extraction.

Current structure (evidence)

Top-level types in EditorView.swift:

Type	Lines	Purpose
EditorView (struct)	181–688	Main SwiftUI view — edit/view mode routing, git history modal, embedded notes sidebar
RawEditor (struct)	692–1073	NSViewRepresentable wrapping LinkAwareTextView
RawEditor.Coordinator (class)	946–1072	NSTextViewDelegate + NSTextStorageDelegate, debounced styling
MarkdownTheme (struct)	1157–1260	Font factory
EditorFontSignature (struct)	1278–1290	Equatable font-change detector
NSAttributedString.Key extension	1293–1304	Custom attribute keys
LinkAwareTextView extension #1	1448–2214	Preview styling, markdown styling (~410 lines at 1640–2050), search highlighting, collapsibles, task checkboxes, inline embeds
LinkAwareTextView (class)	2216–3595	NSTextView subclass — event handling, link/tag tapping, slash commands, table prettification
HTMLToMarkdownConverter (struct)	3596–3768	HTML→markdown paste converter
InlineImageMatch / InlineEmbedMatch / EmbeddedNoteInfo / SidebarEmbedType / SidebarEmbedInfo	3769–3883	DTOs for inline embeds
EmbeddedNotesPanel (struct)	3885–4022	Right-sidebar NSViewRepresentable for embedded note/image previews
FlippedNSView (class)	4025–4027	Y-flipped container
EmbeddedNoteView (class)	4029–4280	Single embedded-note preview
EmbeddedImageView (class)	4300–4780	Image preview with remote fetch via URLSession
CompletionViewController (class)	4780–4896	Wiki-link picker popover
CompletionViewController extensions	4898–4980	NSTableView + NSSearchField delegates
CodeBlockMatch (struct)	4981–4993	Code-block DTO
LinkAwareTextView extension #2	4995–5140	Code-block copy buttons
MarkdownPreviewView (struct)	5142–5436	WKWebView markdown preview

AppState coupling: 61 call sites into appState, of which:

• appState.settings — 19 reads (font family, size, line height, hide-markdown flag)
• Pending-restoration signals (pendingCursorPosition, pendingCursorRange, pendingScrollOffsetY, pendingSearchQuery, pendingCursorTargetPaneIndex) — consumed via consumePending*() helpers at lines 6–36 (read-and-null pattern)
• Direct navigation calls: openFile, openFileInNewTab, openTagInNewTab, switchTab, focusPane, createNote, presentCommandPalette
• Wiki-link picker wired through wikiLinkCompletionHandler / wikiLinkDismissHandler closures stored on AppState

Target file layout

macOS/Synapse/Editor/
 ├── EditorView.swift                  (~400 lines — just the SwiftUI struct)
 ├── RawEditor.swift                   (~250 — NSViewRepresentable only)
 ├── RawEditorCoordinator.swift        (~180 — debounced styling coordinator)
 ├── LinkAwareTextView.swift           (~700 — core NSTextView subclass, event handling)
 ├── LinkAwareTextView+Drawing.swift   (~200 — drawBackground, full-width code bg, blockquote rules)
 ├── LinkAwareTextView+Tracking.swift  (~150 — hover/tracking areas)
 ├── MarkdownStyling.swift             (~500 — applyMarkdownStyling + applyPreviewStyling + MarkdownTheme)
 ├── CollapsibleSections.swift         (~200 — collapsible state manager + toggle buttons)
 ├── CodeBlockCopyButtons.swift        (~150 — copy-button lifecycle)
 ├── WikiLinkPicker.swift              (~300 — CompletionViewController + delegates)
 ├── SlashCommands.swift               (extend existing file — expansion lives here already conceptually)
 ├── InlineEmbeds/
 │    ├── EmbeddedNotesPanel.swift     (~200)
 │    ├── EmbeddedNoteView.swift       (~250)
 │    ├── EmbeddedImageView.swift      (~400 — includes remote fetch)
 │    ├── YouTubePreviewView.swift     (~150)
 │    └── InlineEmbedMatchers.swift    (~100 — regex matching + DTOs)
 ├── GitHistoryModal.swift             (~200 — history UI + loadFileHistory + selectCommit)
 └── MarkdownPreviewView.swift         (~300 — WKWebView + JS bridge)

Approx line totals: 5,436 → ~3,800 across ~15 files (some gains from removing duplicated helpers).

Phased plan

Each phase is one PR, compiles, runs smoke tests from #237 Phase 0, and can be reverted.

Phase 1 — Leaf extractions (safe, no coupling changes)

Move types that have no other types depending on them inside the file:

• MarkdownTheme + EditorFontSignature + NSAttributedString.Key extension → MarkdownStyling.swift
• HTMLToMarkdownConverter → HTMLToMarkdownConverter.swift
• DTOs (InlineImageMatch, InlineEmbedMatch, CodeBlockMatch, EmbeddedNoteInfo, SidebarEmbedType, SidebarEmbedInfo) → InlineEmbeds/InlineEmbedMatchers.swift
• FlippedNSView → co-locate with EmbeddedNotesPanel extraction in Phase 4

Phase 2 — Extract MarkdownPreviewView

• MarkdownPreviewView (5142–5436) is a self-contained NSViewRepresentable over WKWebView.
• Move as-is to MarkdownPreviewView.swift. Done.

Phase 3 — Extract CompletionViewController (wiki-link picker)

• Move CompletionViewController + its extensions (4780–4980) to WikiLinkPicker.swift.
• The wikiLinkCompletionHandler / wikiLinkDismissHandler closures on AppState remain for now — untangling those is deferred to chore: refactor god object #237.

Phase 4 — Extract inline embed views

• EmbeddedNotesPanel, EmbeddedNoteView, EmbeddedImageView, YouTubePreviewView, FlippedNSView each to their own file under InlineEmbeds/.
• Address the unmanaged URLSession in EmbeddedImageView (line ~4646) while it's touched: cancel the data task in removeFromSuperview().

Phase 5 — Extract markdown styling engine

• applyMarkdownStyling() (1640–2050) and applyPreviewStyling() (1474–1630) move to MarkdownStyling.swift as free functions or a MarkdownStyler type taking NSTextStorage + settings snapshot.
• This is the highest-value extraction: makes the styling engine unit-testable against a hand-built NSTextStorage.
• Must keep behavior bit-exact — add golden tests (input markdown → expected attribute runs) before moving.

Phase 6 — Extract code-block copy buttons + collapsible sections

• LinkAwareTextView extension feat: add ability to clone remote repository for notes sync #2 (4995–5140) → CodeBlockCopyButtons.swift.
• Collapsible-section manager + toggle buttons → CollapsibleSections.swift.
• Replace the objc_getAssociatedObject / objc_setAssociatedObject pattern (4997–5003) with a typed wrapper while touching it.

Phase 7 — Split LinkAwareTextView by responsibility

Largest phase. LinkAwareTextView (2216–3595) is ~1,400 lines; split into:

• Core class stays in LinkAwareTextView.swift (event handling, init, properties)
• +Drawing.swift — drawBackground(in:) and full-width backgrounds (2276–2366)
• +Tracking.swift — hover + tracking areas (2400–2450)
• +Search.swift — search highlighting via notifications (2609–2700)
• +SlashCommands.swift — slash-command expansion (3150–3300), merge with existing SlashCommands.swift if possible
• +TablePrettifier.swift — table pretty-printing (3400–3500)

Phase 8 — Extract git history modal

• loadFileHistory(), selectCommit(), and the history modal UI (EditorView 290–505) → GitHistoryModal.swift.
• While there: the synchronous GitService init on main thread (464, 480) and synchronous commit content fetch (487) should be made async.

Phase 9 — Extract RawEditor.Coordinator

• Move RawEditor + its Coordinator to RawEditor.swift + RawEditorCoordinator.swift.
• The debounce interval (80ms, line 1048) becomes a named constant.

Phase 10 — Final cleanup

• EditorView.swift should be <500 lines holding just the SwiftUI view.
• Audit the consumePending*() helpers (lines 6–36) — if chore: refactor god object #237 has moved pending signals to EditorState, update these to read from the store directly. Otherwise leave as-is and delete in the chore: refactor god object #237 follow-up.

Testability milestones

• After Phase 5: MarkdownStyler has golden tests covering headings, code blocks, wiki-links, tags, callouts, blockquotes, frontmatter — runs in <1s, no SwiftUI.
• After Phase 4: EmbeddedImageView can be instantiated in a test window without touching the network (inject the URLSession).
• After Phase 7: LinkAwareTextView responsibilities are file-local; reading any one concern no longer requires scrolling past 1,400 lines.

Concerns to address while touching this code

• Synchronous file reads during styling (lines 3180, 3240, 3333, 3344): String(contentsOf:) / Data(contentsOf:) for inline image resolution. Move to background + cache.
• Synchronous FileManager.fileExists / createFile for debug logging (2198–2205). Delete or gate behind a debug flag.
• Silent git failures (464–467, 480–485) — surface to UI or log properly.
• Recursive collectLinkAwareTextViews() (60–68) has no cycle detection. Unlikely to cycle in practice but worth a depth cap.

Risks

• Bit-exact styling preservation. The markdown styling engine is regex-heavy and visually sensitive. Add golden tests before moving it.
• Objective-C runtime interaction. objc_getAssociatedObject usage must be preserved carefully when extracting — these associations are keyed by static pointer and must stay unique across the split.
• AppState coupling remains. This issue does not decouple EditorView from AppState — that's chore: refactor god object #237's job. The two refactors can proceed in parallel as long as we don't fight over the same file at the same time.

Out of scope

• Decoupling from AppState (tracked in chore: refactor god object #237).
• Rewriting the styling engine (regex → proper parser) — separate issue if desired.
• FileTreeView and SettingsManager breakups — separate issues.