[codex] Workspace diff polish (#6383)

## Thinking Path

> - Paperclip gives operators a workspace diff plugin so they can
inspect agent changes before review
> - The diff view needs reliable base-ref defaults and controls that
stay usable while scrolling large diffs
> - The working branch mixed those plugin improvements with unrelated
server and cloud work
> - Keeping the workspace diff plugin changes isolated makes them easy
to test and review
> - This pull request polishes the workspace diff plugin controls,
base-ref behavior, and sticky headers
> - The benefit is a more predictable diff review surface for agent
workspaces

## What Changed

- Fixed workspace diff default base-ref resolution.
- Improved split/unified and working-tree/against-ref pane controls.
- Made workspace diff headers stay sticky while scrolling.
- Added a review screenshot at
`screenshots/PAP-9841-workspace-diff.png`.

## Verification

- `pnpm install --frozen-lockfile --ignore-scripts`
- `pnpm --filter @paperclipai/plugin-sdk build`
- `pnpm --filter @paperclipai/plugin-workspace-diff exec vitest run
tests/plugin.spec.ts`
- Result: 9 tests passed.

## Risks

- UI-only plugin branch with low data risk.
- The default base-ref inference should be reviewed against unusual
worktree/upstream combinations.

> For core feature work, check [`ROADMAP.md`](ROADMAP.md) first and
discuss it in `#dev` before opening the PR. Feature PRs that overlap
with planned core work may need to be redirected — check the roadmap
first. See `CONTRIBUTING.md`.

## Model Used

- OpenAI Codex, GPT-5-based coding agent with local shell/git/tool use.
Exact hosted model ID and context-window size are not exposed by the
local Paperclip adapter runtime.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/plugins/plugin-workspace-diff/src/ui/index.tsx

@@ -3,7 +3,17 @@ import { usePluginData, usePluginToast } from "@paperclipai/plugin-sdk/ui";
 import { DIFFS_TAG_NAME, getSingularPatch } from "@pierre/diffs";
 import type { PatchDiffProps } from "@pierre/diffs/react";
 import { useFileDiffInstance } from "@pierre/diffs/react";
-import { createElement, type ReactNode, useCallback, useEffect, useMemo, useRef, useState } from "react";
+import {
+  createElement,
+  type KeyboardEvent,
+  type PointerEvent,
+  type ReactNode,
+  useCallback,
+  useEffect,
+  useMemo,
+  useRef,
+  useState,
+} from "react";
 import {
   diffSummary,
   fileName,
@@ -23,6 +33,12 @@ type DiffViewMode = "working-tree" | "head";
 
 type LucideIconProps = { size?: number };
 
+const DEFAULT_FILE_SIDEBAR_WIDTH = 280;
+const MIN_FILE_SIDEBAR_WIDTH = 220;
+const MAX_FILE_SIDEBAR_WIDTH = 520;
+const FILE_SIDEBAR_WIDTH_STEP = 16;
+const FILE_SIDEBAR_WIDTH_STORAGE_KEY = "paperclip.workspace-diff.files-sidebar-width";
+
 function makeLucideIcon(paths: ReactNode) {
   return function LucideIcon({ size = 16 }: LucideIconProps) {
     return (
@@ -57,6 +73,11 @@ function readInitialView(): DiffViewMode {
   return new URLSearchParams(window.location.search).get("diffView") === "head" ? "head" : "working-tree";
 }
 
+function hasInitialViewParam() {
+  if (typeof window === "undefined") return false;
+  return new URLSearchParams(window.location.search).has("diffView");
+}
+
 function readInitialBaseRef() {
   if (typeof window === "undefined") return "";
   return new URLSearchParams(window.location.search).get("baseRef") ?? "";
@@ -80,6 +101,51 @@ function iconButtonClass(active = false) {
   ].join(" ");
 }
 
+function clampFileSidebarWidth(width: number) {
+  return Math.min(MAX_FILE_SIDEBAR_WIDTH, Math.max(MIN_FILE_SIDEBAR_WIDTH, width));
+}
+
+function readStoredFileSidebarWidth() {
+  if (typeof window === "undefined") return DEFAULT_FILE_SIDEBAR_WIDTH;
+
+  try {
+    const stored = window.localStorage.getItem(FILE_SIDEBAR_WIDTH_STORAGE_KEY);
+    if (!stored) return DEFAULT_FILE_SIDEBAR_WIDTH;
+    const parsed = Number.parseInt(stored, 10);
+    return Number.isFinite(parsed) ? clampFileSidebarWidth(parsed) : DEFAULT_FILE_SIDEBAR_WIDTH;
+  } catch {
+    return DEFAULT_FILE_SIDEBAR_WIDTH;
+  }
+}
+
+function writeStoredFileSidebarWidth(width: number) {
+  if (typeof window === "undefined") return;
+
+  try {
+    window.localStorage.setItem(FILE_SIDEBAR_WIDTH_STORAGE_KEY, String(clampFileSidebarWidth(width)));
+  } catch {
+    // Storage can be unavailable; keep resize interactive even when persistence fails.
+  }
+}
+
+function useIsDesktopDiffLayout() {
+  const [isDesktop, setIsDesktop] = useState(() => {
+    if (typeof window === "undefined" || typeof window.matchMedia !== "function") return false;
+    return window.matchMedia("(min-width: 1024px)").matches;
+  });
+
+  useEffect(() => {
+    if (typeof window === "undefined" || typeof window.matchMedia !== "function") return;
+
+    const query = window.matchMedia("(min-width: 1024px)");
+    const update = () => setIsDesktop(query.matches);
+    query.addEventListener("change", update);
+    return () => query.removeEventListener("change", update);
+  }, []);
+
+  return isDesktop;
+}
+
 function warningText(file: DiffFileViewModel) {
   if (file.binary) return "Binary file";
   if (file.oversized) return "Too large to render";
@@ -260,9 +326,11 @@ export function ErrorState({
 function FileDiffPanel({
   file,
   mode,
+  lineWrap,
 }: {
   file: DiffFileViewModel;
   mode: DiffRenderMode;
+  lineWrap: boolean;
 }) {
   const warning = warningText(file);
   if (warning) {
@@ -295,7 +363,7 @@ function FileDiffPanel({
                 patch={patch.patch}
                 options={{
                   diffStyle: mode,
-                  overflow: "scroll",
+                  overflow: lineWrap ? "wrap" : "scroll",
                   disableLineNumbers: false,
                   themeType: "system",
                 }}
@@ -343,25 +411,38 @@ function CollapsedFilePanel({
 export function ChangesTab({ context }: PluginDetailTabProps) {
   const toast = usePluginToast();
   const [mode, setMode] = useState<DiffRenderMode>("split");
+  const [lineWrap, setLineWrap] = useState(false);
   const [view, setView] = useState<DiffViewMode>(() => readInitialView());
   const [baseRef, setBaseRef] = useState(() => readInitialBaseRef());
   const baseRefTouchedRef = useRef(Boolean(baseRef.trim()));
+  const viewTouchedRef = useRef(hasInitialViewParam());
   const [includeUntracked, setIncludeUntracked] = useState(false);
   const [expandedFiles, setExpandedFiles] = useState<Set<string>>(() => new Set());
   const [selectedPath, setSelectedPath] = useState<string | null>(null);
+  const [fileSidebarWidth, setFileSidebarWidth] = useState(() => readStoredFileSidebarWidth());
+  const [fileSidebarResizing, setFileSidebarResizing] = useState(false);
+  const fileSidebarWidthRef = useRef(fileSidebarWidth);
+  const fileSidebarDragRef = useRef<{ startX: number; startWidth: number } | null>(null);
   const fileSectionRefs = useRef(new Map<string, HTMLElement>());
   const diffScrollRef = useRef<HTMLElement | null>(null);
   const scrollSyncFrameRef = useRef<number | null>(null);
+  const usesDesktopDiffLayout = useIsDesktopDiffLayout();
+  const requestedBaseRef = baseRef.trim();
+  const effectiveView = view === "head" && !requestedBaseRef ? "working-tree" : view;
+  const fileSidebarStyle = useMemo(
+    () => usesDesktopDiffLayout ? { width: `${fileSidebarWidth}px` } : undefined,
+    [fileSidebarWidth, usesDesktopDiffLayout],
+  );
 
   const params = useMemo(() => ({
     workspaceId: context.entityId,
     companyId: context.companyId ?? "",
     projectId: context.projectId ?? "",
     entityType: context.entityType,
-    view,
+    view: effectiveView,
-    baseRef: baseRef.trim() || null,
+    baseRef: requestedBaseRef || null,
     includeUntracked,
-  }), [baseRef, context.companyId, context.entityId, context.entityType, context.projectId, includeUntracked, view]);
+  }), [context.companyId, context.entityId, context.entityType, context.projectId, effectiveView, includeUntracked, requestedBaseRef]);
 
   const { data, loading, error, refresh } = usePluginData<WorkspaceDiffData>("workspace-diff", params);
   const files = useMemo(() => toFileViewModels(data), [data]);
@@ -414,11 +495,70 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
     });
   }, [syncSelectedPathFromScroll]);
 
+  const commitFileSidebarWidth = useCallback((nextWidth: number) => {
+    const clamped = clampFileSidebarWidth(nextWidth);
+    fileSidebarWidthRef.current = clamped;
+    setFileSidebarWidth(clamped);
+    writeStoredFileSidebarWidth(clamped);
+  }, []);
+
+  const handleFileSidebarPointerDown = useCallback((event: PointerEvent<HTMLDivElement>) => {
+    if (!usesDesktopDiffLayout) return;
+
+    event.preventDefault();
+    event.currentTarget.setPointerCapture(event.pointerId);
+    fileSidebarDragRef.current = {
+      startX: event.clientX,
+      startWidth: fileSidebarWidthRef.current,
+    };
+    setFileSidebarResizing(true);
+  }, [usesDesktopDiffLayout]);
+
+  const handleFileSidebarPointerMove = useCallback((event: PointerEvent<HTMLDivElement>) => {
+    const drag = fileSidebarDragRef.current;
+    if (!drag) return;
+
+    const nextWidth = clampFileSidebarWidth(drag.startWidth + event.clientX - drag.startX);
+    fileSidebarWidthRef.current = nextWidth;
+    setFileSidebarWidth(nextWidth);
+  }, []);
+
+  const endFileSidebarResize = useCallback(() => {
+    if (!fileSidebarDragRef.current) return;
+
+    fileSidebarDragRef.current = null;
+    setFileSidebarResizing(false);
+    writeStoredFileSidebarWidth(fileSidebarWidthRef.current);
+  }, []);
+
+  const handleFileSidebarKeyDown = useCallback((event: KeyboardEvent<HTMLDivElement>) => {
+    if (!usesDesktopDiffLayout) return;
+
+    if (event.key === "ArrowLeft") {
+      event.preventDefault();
+      commitFileSidebarWidth(fileSidebarWidth - FILE_SIDEBAR_WIDTH_STEP);
+    } else if (event.key === "ArrowRight") {
+      event.preventDefault();
+      commitFileSidebarWidth(fileSidebarWidth + FILE_SIDEBAR_WIDTH_STEP);
+    } else if (event.key === "Home") {
+      event.preventDefault();
+      commitFileSidebarWidth(MIN_FILE_SIDEBAR_WIDTH);
+    } else if (event.key === "End") {
+      event.preventDefault();
+      commitFileSidebarWidth(MAX_FILE_SIDEBAR_WIDTH);
+    }
+  }, [commitFileSidebarWidth, fileSidebarWidth, usesDesktopDiffLayout]);
+
   useEffect(() => {
     const defaultBaseRef = data?.defaultBaseRef?.trim();
-    if (!defaultBaseRef || baseRef.trim() || baseRefTouchedRef.current) return;
+    if (!defaultBaseRef) return;
-    setBaseRef(defaultBaseRef);
+    if (!baseRef.trim() && !baseRefTouchedRef.current) {
-  }, [baseRef, data?.defaultBaseRef]);
+      setBaseRef(defaultBaseRef);
+    }
+    if (view === "working-tree" && !viewTouchedRef.current) {
+      setView("head");
+    }
+  }, [baseRef, data?.defaultBaseRef, view]);
 
   useEffect(() => {
     if (files.length === 0) {
@@ -438,6 +578,19 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
     };
   }, []);
 
+  useEffect(() => {
+    if (!fileSidebarResizing || typeof document === "undefined") return;
+
+    const previousCursor = document.body.style.cursor;
+    const previousUserSelect = document.body.style.userSelect;
+    document.body.style.cursor = "col-resize";
+    document.body.style.userSelect = "none";
+    return () => {
+      document.body.style.cursor = previousCursor;
+      document.body.style.userSelect = previousUserSelect;
+    };
+  }, [fileSidebarResizing]);
+
   const copyPath = async (filePath: string) => {
     try {
       await navigator.clipboard.writeText(filePath);
@@ -475,11 +628,37 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
               Unified
             </button>
           </div>
+          <button
+            key="line-wrap"
+            type="button"
+            className={buttonClass(lineWrap)}
+            onClick={() => setLineWrap((value) => !value)}
+            title={lineWrap ? "Disable line wrapping" : "Enable line wrapping"}
+            aria-pressed={lineWrap}
+          >
+            {lineWrap ? "Wrap on" : "Wrap lines"}
+          </button>
           <div key="view" className="inline-flex gap-1" aria-label="Diff comparison">
-            <button key="working-tree" type="button" className={buttonClass(view === "working-tree")} onClick={() => setView("working-tree")}>
+            <button
+              key="working-tree"
+              type="button"
+              className={buttonClass(effectiveView === "working-tree")}
+              onClick={() => {
+                viewTouchedRef.current = true;
+                setView("working-tree");
+              }}
+            >
               Working tree
             </button>
-            <button key="head" type="button" className={buttonClass(view === "head")} onClick={() => setView("head")}>
+            <button
+              key="head"
+              type="button"
+              className={buttonClass(effectiveView === "head")}
+              onClick={() => {
+                viewTouchedRef.current = true;
+                setView("head");
+              }}
+            >
               Against ref
             </button>
           </div>
@@ -526,8 +705,12 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
       ) : files.length === 0 ? (
         <EmptyState />
       ) : (
-        <div key="content" className="grid gap-3 lg:h-[70vh] lg:min-h-[560px] lg:max-h-[820px] lg:grid-cols-[280px_minmax(0,1fr)]">
+        <div key="content" className="flex flex-col gap-3 lg:h-[70vh] lg:min-h-[560px] lg:max-h-[820px] lg:flex-row">
-          <aside key="files" className="flex min-w-0 flex-col border border-border bg-background lg:h-full lg:overflow-hidden">
+          <aside
+            key="files"
+            className="relative flex min-w-0 flex-col border border-border bg-background lg:h-full lg:shrink-0 lg:overflow-hidden"
+            style={fileSidebarStyle}
+          >
             <div key="heading" className="border-b border-border px-3 py-2 text-xs font-medium uppercase tracking-[0.14em] text-muted-foreground">
               Files
             </div>
@@ -544,12 +727,33 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
                 />
               ))}
             </div>
+            <div
+              role="separator"
+              aria-label="Resize file list"
+              aria-orientation="vertical"
+              aria-valuemin={MIN_FILE_SIDEBAR_WIDTH}
+              aria-valuemax={MAX_FILE_SIDEBAR_WIDTH}
+              aria-valuenow={fileSidebarWidth}
+              tabIndex={0}
+              className={[
+                "absolute inset-y-0 right-0 z-20 hidden w-3 cursor-col-resize touch-none outline-none lg:block",
+                "before:absolute before:inset-y-0 before:left-1/2 before:w-px before:-translate-x-1/2 before:bg-transparent before:transition-colors",
+                "hover:before:bg-border focus-visible:before:bg-ring",
+                fileSidebarResizing ? "before:bg-ring" : "",
+              ].join(" ")}
+              onPointerDown={handleFileSidebarPointerDown}
+              onPointerMove={handleFileSidebarPointerMove}
+              onPointerUp={endFileSidebarResize}
+              onPointerCancel={endFileSidebarResize}
+              onLostPointerCapture={endFileSidebarResize}
+              onKeyDown={handleFileSidebarKeyDown}
+            />
           </aside>
 
           <main
             key="diffs"
             ref={diffScrollRef}
-            className="max-h-[70vh] min-w-0 space-y-3 overflow-auto lg:h-full lg:max-h-none lg:pr-1"
+            className="max-h-[70vh] min-w-0 flex-1 space-y-3 overflow-auto lg:h-full lg:max-h-none lg:pr-1"
             onScroll={handleDiffScroll}
           >
             {files
@@ -559,7 +763,10 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
                   ref={setFileSectionRef(file.path)}
                   className={file.path === selectedFile?.path ? "scroll-mt-2" : undefined}
                 >
-                  <div key="header" className="flex min-w-0 items-center justify-between gap-3 border border-b-0 border-border bg-muted/35 px-3 py-2">
+                  <div
+                    key="header"
+                    className="sticky top-0 z-30 flex min-w-0 items-center justify-between gap-3 border border-b-0 border-border bg-background px-3 py-2 shadow-sm"
+                  >
                     <div key="left" className="flex min-w-0 items-start gap-2">
                       <button
                         key="collapse"
@@ -599,7 +806,7 @@ export function ChangesTab({ context }: PluginDetailTabProps) {
                     </div>
                   </div>
                   {expandedFiles.has(file.path) ? (
-                    <FileDiffPanel key="diff" file={file} mode={mode} />
+                    <FileDiffPanel key="diff" file={file} mode={mode} lineWrap={lineWrap} />
                   ) : (
                     <CollapsedFilePanel
                       key="collapsed"

packages/plugins/plugin-workspace-diff/src/worker.ts

@@ -1,4 +1,4 @@
-import { definePlugin, runWorker } from "@paperclipai/plugin-sdk";
+import { definePlugin, runWorker, type PluginContext } from "@paperclipai/plugin-sdk";
 import { workspaceDiffQuerySchema } from "./contracts.js";
 import { workspaceDiffService } from "./workspace-diff.js";
 
@@ -23,6 +23,25 @@ export function resolveDefaultBaseRef(input: {
     ?? readOptionalString(input.projectWorkspaceRepoRef);
 }
 
+async function resolveProjectWorkspaceDefaultBaseRef(input: {
+  ctx: PluginContext;
+  projectId: string;
+  companyId: string;
+  projectWorkspaceId?: string | null;
+}): Promise<string | null> {
+  if (!input.projectId) return null;
+  const workspaces = await input.ctx.projects.listWorkspaces(input.projectId, input.companyId);
+  const projectWorkspace = input.projectWorkspaceId
+    ? workspaces.find((candidate) => candidate.id === input.projectWorkspaceId)
+    : workspaces.find((candidate) => candidate.isPrimary) ?? workspaces[0] ?? null;
+  return projectWorkspace
+    ? resolveDefaultBaseRef({
+      projectWorkspaceDefaultRef: projectWorkspace.defaultRef,
+      projectWorkspaceRepoRef: projectWorkspace.repoRef,
+    })
+    : null;
+}
+
 const plugin = definePlugin({
   async setup(ctx) {
     ctx.logger.info(`${PLUGIN_NAME} plugin setup`);
@@ -61,15 +80,13 @@ const plugin = definePlugin({
         throw new Error("Workspace not found");
       }
       let projectWorkspaceDefaultBaseRef: string | null = null;
-      if (!readOptionalString(workspace.baseRef) && workspace.projectWorkspaceId) {
+      if (!readOptionalString(workspace.baseRef)) {
-        const workspaces = await ctx.projects.listWorkspaces(workspace.projectId, companyId);
+        projectWorkspaceDefaultBaseRef = await resolveProjectWorkspaceDefaultBaseRef({
-        const projectWorkspace = workspaces.find((candidate) => candidate.id === workspace.projectWorkspaceId);
+          ctx,
-        projectWorkspaceDefaultBaseRef = projectWorkspace
+          projectId: workspace.projectId || readString(params.projectId),
-          ? resolveDefaultBaseRef({
+          companyId,
-            projectWorkspaceDefaultRef: projectWorkspace.defaultRef,
+          projectWorkspaceId: workspace.projectWorkspaceId,
-            projectWorkspaceRepoRef: projectWorkspace.repoRef,
+        });
-          })
-          : null;
       }
 
       return workspaceDiff.getDiff({

packages/plugins/plugin-workspace-diff/src/workspace-diff.ts

@@ -645,6 +645,57 @@ async function resolveHeadSha(cwd: string) {
   }
 }
 
+async function resolveVerifiedGitRef(cwd: string, refName: string) {
+  const trimmed = refName.trim();
+  if (!trimmed) return null;
+  try {
+    await execFileAsync("git", ["-C", cwd, "rev-parse", "--verify", "--quiet", `${trimmed}^{commit}`], {
+      cwd,
+      timeout: GIT_TIMEOUT_MS,
+      maxBuffer: 128 * 1024,
+    });
+    return trimmed;
+  } catch {
+    return null;
+  }
+}
+
+async function resolveGitUpstreamRef(cwd: string) {
+  try {
+    const upstream = (await execFileAsync(
+      "git",
+      ["-C", cwd, "rev-parse", "--abbrev-ref", "--symbolic-full-name", "@{upstream}"],
+      {
+        cwd,
+        timeout: GIT_TIMEOUT_MS,
+        maxBuffer: 128 * 1024,
+      },
+    )).stdout.trim();
+    return upstream ? await resolveVerifiedGitRef(cwd, upstream) : null;
+  } catch {
+    return null;
+  }
+}
+
+async function resolveInferredDefaultBaseRef(cwd: string) {
+  const upstream = await resolveGitUpstreamRef(cwd);
+  if (upstream) return upstream;
+
+  const candidates = ["origin/master", "origin/main", "master", "main"];
+  const resolvedCandidates = await Promise.all(
+    candidates.map((candidate) => resolveVerifiedGitRef(cwd, candidate)),
+  );
+  for (const resolved of resolvedCandidates) {
+    if (resolved) return resolved;
+  }
+
+  return null;
+}
+
+async function resolveDefaultDiffBaseRef(cwd: string, workspace: WorkspaceDiffTarget) {
+  return workspace.baseRef?.trim() || await resolveInferredDefaultBaseRef(cwd);
+}
+
 async function resolveBaseRef(cwd: string, baseRef: string | null, workspace: WorkspaceDiffTarget) {
   const resolvedBaseRef = baseRef ?? workspace.baseRef ?? null;
   if (!resolvedBaseRef) {
@@ -705,9 +756,16 @@ export function workspaceDiffService() {
   return {
     async getDiff(workspace: WorkspaceDiffTarget, query: WorkspaceDiffQueryOptions): Promise<WorkspaceDiffResponse> {
       const { cwd, repoRoot } = await resolveWorkspacePaths(workspace);
+      const defaultBaseRef = await resolveDefaultDiffBaseRef(cwd, workspace);
+      const workspaceWithDefaultBaseRef = { ...workspace, baseRef: defaultBaseRef };
       const paths = normalizePathFilters(query.paths);
       const warnings: WorkspaceDiffWarning[] = [];
-      const { files: filesByPath, baseRef } = await collectFiles({ cwd, workspace, query, paths });
+      const { files: filesByPath, baseRef } = await collectFiles({
+        cwd,
+        workspace: workspaceWithDefaultBaseRef,
+        query,
+        paths,
+      });
       const allFiles = Array.from(filesByPath.values()).sort((left, right) => left.path.localeCompare(right.path));
       const cappedFiles = allFiles.slice(0, WORKSPACE_DIFF_CAPS.maxFiles);
       if (allFiles.length > cappedFiles.length) {
@@ -771,7 +829,7 @@ export function workspaceDiffService() {
         companyId: workspace.companyId,
         view: query.view,
         baseRef,
-        defaultBaseRef: workspace.baseRef,
+        defaultBaseRef,
         headSha: await resolveHeadSha(cwd),
         includeUntracked: query.includeUntracked,
         paths,

packages/plugins/plugin-workspace-diff/tests/plugin.spec.ts

@@ -227,6 +227,115 @@ describe("workspace diff plugin", () => {
     });
   });
 
+  it("uses the primary project workspace default ref when execution workspace has no workspace link", async () => {
+    const root = await createGitWorkspace();
+    await git(root, ["checkout", "-b", "feature"]);
+    await fs.writeFile(path.join(root, "src/app.ts"), "export const value = 5;\n");
+    await git(root, ["add", "src/app.ts"]);
+    await git(root, ["commit", "-m", "feature change"]);
+    const harness = createTestHarness({ manifest });
+    harness.seed({
+      executionWorkspaces: [{
+        id: "workspace-1",
+        companyId: "company-1",
+        projectId: "project-1",
+        projectWorkspaceId: null,
+        path: root,
+        cwd: root,
+        repoUrl: null,
+        baseRef: null,
+        branchName: "feature",
+        providerType: "git_worktree",
+        providerMetadata: null,
+      }],
+    });
+    harness.ctx.projects.listWorkspaces = async (projectId, companyId) => {
+      expect(projectId).toBe("project-1");
+      expect(companyId).toBe("company-1");
+      return [{
+        id: "project-workspace-1",
+        projectId: "project-1",
+        name: "Primary",
+        path: root,
+        repoUrl: null,
+        repoRef: "feature",
+        defaultRef: "main",
+        isPrimary: true,
+        createdAt: new Date().toISOString(),
+        updatedAt: new Date().toISOString(),
+      }];
+    };
+    await plugin.definition.setup(harness.ctx);
+
+    const result = await harness.getData("workspace-diff", {
+      workspaceId: "workspace-1",
+      companyId: "company-1",
+      projectId: "project-1",
+      view: "head",
+      baseRef: null,
+      includeUntracked: false,
+    });
+
+    expect(result).toMatchObject({
+      baseRef: "main",
+      defaultBaseRef: "main",
+      stats: { fileCount: 1 },
+      files: [expect.objectContaining({ path: "src/app.ts" })],
+    });
+  });
+
+  it("infers the default base ref from the execution workspace branch upstream", async () => {
+    const root = await createGitWorkspace();
+    await git(root, ["update-ref", "refs/remotes/origin/master", "HEAD"]);
+    await git(root, ["checkout", "-b", "feature"]);
+    await git(root, ["config", "branch.feature.remote", "origin"]);
+    await git(root, ["config", "branch.feature.merge", "refs/heads/master"]);
+    await fs.writeFile(path.join(root, "src/app.ts"), "export const value = 6;\n");
+    await git(root, ["add", "src/app.ts"]);
+    await git(root, ["commit", "-m", "feature change"]);
+    const harness = createTestHarness({ manifest });
+    harness.seed({
+      executionWorkspaces: [{
+        id: "workspace-1",
+        companyId: "company-1",
+        projectId: "project-1",
+        projectWorkspaceId: null,
+        path: root,
+        cwd: root,
+        repoUrl: null,
+        baseRef: null,
+        branchName: "feature",
+        providerType: "git_worktree",
+        providerMetadata: null,
+      }],
+    });
+    await plugin.definition.setup(harness.ctx);
+
+    await expect(harness.getData("workspace-diff", {
+      workspaceId: "workspace-1",
+      companyId: "company-1",
+      view: "working-tree",
+      includeUntracked: false,
+    })).resolves.toMatchObject({
+      baseRef: null,
+      defaultBaseRef: "origin/master",
+      stats: { fileCount: 0 },
+    });
+
+    await expect(harness.getData("workspace-diff", {
+      workspaceId: "workspace-1",
+      companyId: "company-1",
+      view: "head",
+      baseRef: null,
+      includeUntracked: false,
+    })).resolves.toMatchObject({
+      baseRef: "origin/master",
+      defaultBaseRef: "origin/master",
+      stats: { fileCount: 1 },
+      files: [expect.objectContaining({ path: "src/app.ts" })],
+    });
+  });
+
   it("returns a clear bridge error when required context is missing", async () => {
     const harness = createTestHarness({ manifest });
     await plugin.definition.setup(harness.ctx);