fix(engine): silence PERF logs by default, fix "modifying state during view update"

PerfTrace was opt-out (MD_PERF=0 to silence) so every Debug build
printed a PERF line per keystroke unconditionally. Flipped to opt-in
(MD_PERF=1 to enable) - still fully available for future perf work,
just quiet by default.

"Modifying state during view update": onCodeBlockSelectionChange,
onSelectedTextChange, and onCommentAnchorRectsChange could all fire
synchronously from inside NativeTextViewWrapper.updateNSView's own
call stack - a programmatic edit (pendingInlineReplacement/
pendingTextInsertion/pendingTextRangeReplacement) re-enters
textViewDidChangeSelection/textDidChange synchronously (AppKit resets
selection on edit), which is still a SwiftUI view update in progress.
Calling straight into the embedder's @State setter there is exactly
what trips the warning. Routed all three through new
fireCodeBlockSelectionChange/fireSelectedTextChange/
fireCommentAnchorRectsChange helpers on the coordinator that defer
one runloop tick via DispatchQueue.main.async - same technique
NativeTextViewWrapper already uses to clear its own pending*
bindings, just centralized instead of ad-hoc per call site.

322/322 tests passing.

Vendor/swift-markdown-engine/Sources/MarkdownEngine/Diagnostics/PerfTrace.swift

@@ -9,7 +9,9 @@
 //  which costs grow with file size instead of staying constant. The whole point:
 //  type in a short file, then a long one, and compare `total` for the same edit.
 //
-//  Toggle: set the env var MD_PERF=0 in the run scheme to silence.
+//  Toggle: set the env var MD_PERF=1 in the run scheme to enable.
+//  Off by default even in Debug — opt-in, not opt-out, so a normal
+//  debug run stays quiet.
 //  Debug-only — the whole thing compiles out in Release.
 //  Remove before shipping (this file + the `PerfTrace.` call sites).
 //
@@ -18,7 +20,7 @@ import Foundation
 
 enum PerfTrace {
 #if DEBUG
-    static var enabled = ProcessInfo.processInfo.environment["MD_PERF"] != "0"
+    static var enabled = ProcessInfo.processInfo.environment["MD_PERF"] == "1"
     /// Opt-in for the sampled full-rebuild verifier asserts (wiki splice,
     /// backtick census, parse buffer). They run 3× O(doc) work synchronously
     /// on every 64th keystroke — periodic spikes that pollute the PERF

Vendor/swift-markdown-engine/Sources/MarkdownEngine/TextView/Coordinator/NativeTextViewCoordinator+CodeBlocks.swift

@@ -15,7 +15,7 @@ import AppKit
 extension NativeTextViewCoordinator {
     func updateCodeBlockSelection(textView: NSTextView, parsed: ParsedDocument? = nil) {
         guard let textContainer = textView.textContainer else {
-            onCodeBlockSelectionChange?([])
+            fireCodeBlockSelectionChange([])
             return
         }
 
@@ -24,7 +24,7 @@ extension NativeTextViewCoordinator {
             // no per-call full-token filter.
             cachedCodeBlockTokens = parsed.codeBlockTokensWithIndices
         } else if cachedCodeBlockTokens.isEmpty {
-            onCodeBlockSelectionChange?([])
+            fireCodeBlockSelectionChange([])
             return
         }
 
@@ -91,6 +91,6 @@ extension NativeTextViewCoordinator {
             )
         }
 
-        onCodeBlockSelectionChange?(selections)
+        fireCodeBlockSelectionChange(selections)
     }
 }

Vendor/swift-markdown-engine/Sources/MarkdownEngine/TextView/Coordinator/NativeTextViewCoordinator+CommentAnchors.swift

@@ -16,7 +16,7 @@ import AppKit
 extension NativeTextViewCoordinator {
     func updateCommentAnchorRects(textView: NSTextView) {
         guard !commentAnchorQueries.isEmpty else {
-            onCommentAnchorRectsChange?([])
+            fireCommentAnchorRectsChange([])
             return
         }
         let nsText = textView.string as NSString
@@ -28,6 +28,6 @@ extension NativeTextViewCoordinator {
                   let rect = textView.viewRect(forCharacterRange: found, using: layoutBridge) else { continue }
             results.append(CommentAnchorRect(id: query.id, rect: rect))
         }
-        onCommentAnchorRectsChange?(results)
+        fireCommentAnchorRectsChange(results)
     }
 }

Vendor/swift-markdown-engine/Sources/MarkdownEngine/TextView/Coordinator/NativeTextViewCoordinator+TextDelegate.swift

@@ -362,7 +362,7 @@ extension NativeTextViewCoordinator {
         // selection at all.
         if !isRebuildingDocument {
             let selRange = tv.selectedRange()
-            onSelectedTextChange?(selRange.length > 0 ? (tv.string as NSString).substring(with: selRange) : nil)
+            fireSelectedTextChange(selRange.length > 0 ? (tv.string as NSString).substring(with: selRange) : nil)
         }
         // Raw mode: plain source — no reveal, snap-back, or inline previews.
         if configuration.rawSourceMode { return }

Vendor/swift-markdown-engine/Sources/MarkdownEngine/TextView/Coordinator/NativeTextViewCoordinator.swift

@@ -87,6 +87,26 @@ public final class NativeTextViewCoordinator: NSObject, NSTextViewDelegate {
     var onSelectedTextChange: ((String?) -> Void)?
     var commentAnchorQueries: [CommentAnchorQuery] = []
     var onCommentAnchorRectsChange: (([CommentAnchorRect]) -> Void)?
+
+    /// These three callbacks can fire from inside `NativeTextViewWrapper.updateNSView`
+    /// itself (a programmatic edit re-enters `textViewDidChangeSelection`/
+    /// `textDidChange` synchronously — see `isRebuildingDocument` above), which is a
+    /// SwiftUI view update already in progress on the call stack. Calling straight into
+    /// an embedder's `@State` setter there trips "Modifying state during view update" —
+    /// deferring one runloop tick is enough to land outside it, same as how
+    /// `NativeTextViewWrapper` already clears its `pending*` bindings.
+    func fireCodeBlockSelectionChange(_ selections: [CodeBlockSelection]) {
+        DispatchQueue.main.async { [onCodeBlockSelectionChange] in onCodeBlockSelectionChange?(selections) }
+    }
+
+    func fireSelectedTextChange(_ text: String?) {
+        DispatchQueue.main.async { [onSelectedTextChange] in onSelectedTextChange?(text) }
+    }
+
+    func fireCommentAnchorRectsChange(_ rects: [CommentAnchorRect]) {
+        DispatchQueue.main.async { [onCommentAnchorRectsChange] in onCommentAnchorRectsChange?(rects) }
+    }
+
     var didInitialFormatting: Bool = false
     /// One-shot guard so `updateCodeBlockSelection` only forces a full-document layout once per document.
     var didEnsureLayoutForCurrentDocument: Bool = false