Resolve settings display and selection diff design issues

src/features/selection-rewrite/diff.ts

@@ -14,6 +14,8 @@ export function buildSelectionUnifiedDiff(filePath: string, originalText: string
   ].join("\n");
 }
 
+const MAX_SELECTION_REWRITE_LCS_CELLS = 40_000;
+
 interface DiffLine {
   prefix: " " | "+" | "-";
   text: string;
@@ -27,6 +29,10 @@ function textLines(text: string): string[] {
 }
 
 function lineChanges(originalLines: string[], replacementLines: string[]): DiffLine[] {
+  if (originalLines.length * replacementLines.length > MAX_SELECTION_REWRITE_LCS_CELLS) {
+    return linearLineChanges(originalLines, replacementLines);
+  }
+
   const lengths = lcsLengths(originalLines, replacementLines);
   const changes: DiffLine[] = [];
   let oldIndex = 0;
@@ -52,6 +58,45 @@ function lineChanges(originalLines: string[], replacementLines: string[]): DiffL
   return changes.length > 0 ? changes : [{ prefix: " ", text: "" }];
 }
 
+function linearLineChanges(originalLines: string[], replacementLines: string[]): DiffLine[] {
+  const prefixLength = commonPrefixLength(originalLines, replacementLines);
+  const suffixLength = commonSuffixLength(originalLines, replacementLines, prefixLength);
+  const changes: DiffLine[] = [];
+
+  pushLines(changes, " ", originalLines, 0, prefixLength);
+  pushLines(changes, "-", originalLines, prefixLength, originalLines.length - suffixLength);
+  pushLines(changes, "+", replacementLines, prefixLength, replacementLines.length - suffixLength);
+  pushLines(changes, " ", originalLines, originalLines.length - suffixLength, originalLines.length);
+
+  return changes.length > 0 ? changes : [{ prefix: " ", text: "" }];
+}
+
+function commonPrefixLength(left: string[], right: string[]): number {
+  let prefixLength = 0;
+  while (prefixLength < left.length && prefixLength < right.length && left[prefixLength] === right[prefixLength]) {
+    prefixLength += 1;
+  }
+  return prefixLength;
+}
+
+function commonSuffixLength(left: string[], right: string[], prefixLength: number): number {
+  let suffixLength = 0;
+  while (
+    suffixLength < left.length - prefixLength &&
+    suffixLength < right.length - prefixLength &&
+    left[left.length - 1 - suffixLength] === right[right.length - 1 - suffixLength]
+  ) {
+    suffixLength += 1;
+  }
+  return suffixLength;
+}
+
+function pushLines(changes: DiffLine[], prefix: DiffLine["prefix"], lines: string[], start: number, end: number): void {
+  for (let index = start; index < end; index += 1) {
+    changes.push({ prefix, text: lines[index] ?? "" });
+  }
+}
+
 function lcsLengths(left: string[], right: string[]): number[][] {
   const rows = Array.from({ length: left.length + 1 }, () => Array.from({ length: right.length + 1 }, () => 0));
   for (let leftIndex = left.length - 1; leftIndex >= 0; leftIndex -= 1) {

src/settings/dynamic-sections-controller.ts

@@ -13,12 +13,10 @@ import {
 } from "./lifecycle";
 
 interface SettingsDynamicSectionsControllerCallbacks {
-  display(target: SettingsDynamicSectionsDisplayTarget): void;
+  display(): void;
   notify(message: string): void;
 }
 
-type SettingsDynamicSectionsDisplayTarget = "all" | "helper" | "archived" | "hooks";
-
 export interface SettingsDynamicSectionsSnapshot {
   archivedThreads: readonly Thread[];
   archivedThreadsLifecycle: SettingsDynamicSectionLifecycleState;
@@ -119,7 +117,7 @@ export class SettingsDynamicSectionsController {
     const observedModels = observedValue(result);
     if (!observedModels) return;
     this.models = [...observedModels];
-    this.callbacks.display("helper");
+    this.callbacks.display();
   }
 
   private receiveObservedArchivedThreadsResult(result: ObservedResult<readonly Thread[]>): void {
@@ -134,7 +132,7 @@ export class SettingsDynamicSectionsController {
         operationToken: this.archivedThreadsOperationToken,
       });
     }
-    this.callbacks.display("archived");
+    this.callbacks.display();
   }
 
   async refreshDynamicSections(options: { forceModels?: boolean } = {}): Promise<void> {
@@ -158,7 +156,7 @@ export class SettingsDynamicSectionsController {
       status: "Loading hooks...",
       operationToken: hooksOperationToken,
     });
-    this.callbacks.display("all");
+    this.callbacks.display();
 
     let failedCount = 0;
     try {
@@ -261,7 +259,7 @@ export class SettingsDynamicSectionsController {
         if (failedCount > 0) {
           this.callbacks.notify("Could not refresh all Codex details.");
         }
-        this.callbacks.display("all");
+        this.callbacks.display();
       }
     }
   }
@@ -435,7 +433,7 @@ export class SettingsDynamicSectionsController {
         operationToken,
       }),
     );
-    this.callbacks.display(displayTargetForDynamicOperationSection(options.section));
+    this.callbacks.display();
     try {
       await options.operation(operationToken);
     } catch (error) {
@@ -449,7 +447,7 @@ export class SettingsDynamicSectionsController {
       );
       this.callbacks.notify(options.failureNotice);
     } finally {
-      if (!stale()) this.callbacks.display(displayTargetForDynamicOperationSection(options.section));
+      if (!stale()) this.callbacks.display();
     }
   }
 
@@ -490,10 +488,6 @@ export class SettingsDynamicSectionsController {
   }
 }
 
-function displayTargetForDynamicOperationSection(section: "hooks" | "archivedThreads"): SettingsDynamicSectionsDisplayTarget {
-  return section === "hooks" ? "hooks" : "archived";
-}
-
 function archivedThreadsStatus(count: number): string {
   return `Loaded ${String(count)} archived thread${count === 1 ? "" : "s"}.`;
 }

tests/features/selection-rewrite/selection-rewrite.test.ts

@@ -133,6 +133,32 @@ describe("selection rewrite diff", () => {
     );
   });
 
+  it("bounds large selection diffs to a linear prefix and suffix comparison", () => {
+    const originalText = [
+      "same start",
+      ...Array.from({ length: 160 }, (_unused, index) => `old before ${String(index)}`),
+      "shared middle",
+      ...Array.from({ length: 160 }, (_unused, index) => `old after ${String(index)}`),
+      "same end",
+    ].join("\n");
+    const replacementText = [
+      "same start",
+      ...Array.from({ length: 160 }, (_unused, index) => `new before ${String(index)}`),
+      "shared middle",
+      ...Array.from({ length: 160 }, (_unused, index) => `new after ${String(index)}`),
+      "same end",
+    ].join("\n");
+
+    const diff = buildSelectionUnifiedDiff("Note.md", originalText, replacementText);
+
+    expect(diff).toContain("\n same start\n");
+    expect(diff).toContain("\n-old before 0\n");
+    expect(diff).toContain("\n-shared middle\n");
+    expect(diff).toContain("\n+shared middle\n");
+    expect(diff).toContain("\n same end");
+    expect(diff).not.toContain("\n shared middle\n");
+  });
+
   it("renders additions and deletions", () => {
     expect(buildSelectionUnifiedDiff("Note.md", "", "added")).toContain("+added");
     expect(buildSelectionUnifiedDiff("Note.md", "removed", "")).toContain("-removed");

tests/settings/settings-tab.test.ts

@@ -300,7 +300,7 @@ describe("settings tab", () => {
 
     expect(controller.snapshot().archivedThreads.map((thread) => thread.preview)).toEqual(["Archived elsewhere"]);
     expect(controller.snapshot().archivedThreadsLifecycle.kind).toBe("loaded");
-    expect(display).toHaveBeenCalledWith("archived");
+    expect(display).toHaveBeenCalledOnce();
   });
 
   it("ignores stale dynamic sections refresh results after a newer refresh completes", async () => {