diff --git a/src/client/src/appActions.test.ts b/src/client/src/appActions.test.ts
deleted file mode 100644
index 53caf64..0000000
--- a/src/client/src/appActions.test.ts
+++ /dev/null
@@ -1,102 +0,0 @@
-import { describe, expect, it, vi } from "vitest";
-import { createAppActions } from "./appActions";
-import { initialAppState, type AppState } from "./appState";
-import type { SessionInfo } from "./api";
-
-function createContext(statePatch: Partial<AppState> = {}) {
-  const calls: string[] = [];
-  const context = {
-    state: { ...initialAppState(), ...statePatch },
-    openActionPalette: vi.fn(() => { calls.push("openActionPalette"); }),
-    focusPrompt: vi.fn(() => { calls.push("focusPrompt"); }),
-    addProject: vi.fn(() => { calls.push("addProject"); }),
-    selectMainView: vi.fn((view: AppState["mainView"]) => { calls.push(`selectMainView:${view}`); }),
-    refreshFiles: vi.fn(() => { calls.push("refreshFiles"); }),
-    refreshGit: vi.fn(() => { calls.push("refreshGit"); }),
-    startSession: vi.fn(() => { calls.push("startSession"); }),
-    archiveSession: vi.fn(() => { calls.push("archiveSession"); }),
-    stopActiveWork: vi.fn(() => { calls.push("stopActiveWork"); }),
-  };
-  return { context, calls };
-}
-
-describe("createAppActions", () => {
-  it("disables workspace and session actions when no workspace/session is selected", () => {
-    const { context } = createContext();
-    const actions = createAppActions(context);
-
-    expect(actions.find((action) => action.id === "view.files")?.enabled).toBe(false);
-    expect(actions.find((action) => action.id === "session.start")?.enabled).toBe(false);
-    expect(actions.find((action) => action.id === "session.archive")?.enabled).toBe(false);
-    expect(actions.find((action) => action.id === "session.stop")?.enabled).toBe(false);
-    expect(actions.find((action) => action.id === "actions.show")?.enabled).toBeUndefined();
-  });
-
-  it("enables workspace actions when a workspace is selected", () => {
-    const { context } = createContext({ selectedWorkspace: testWorkspace() });
-    const actions = createAppActions(context);
-
-    expect(actions.find((action) => action.id === "view.files")?.enabled).toBe(true);
-    expect(actions.find((action) => action.id === "session.start")?.enabled).toBe(true);
-  });
-
-  it("routes refresh current to the active workspace tool", () => {
-    const { context, calls } = createContext({
-      selectedWorkspace: testWorkspace(),
-      workspaceTool: "git",
-    });
-    const action = createAppActions(context).find((candidate) => candidate.id === "workspace.refresh-current");
-
-    if (action !== undefined) void action.run();
-
-    expect(calls).toEqual(["refreshGit"]);
-  });
-
-  it("enables archive for the selected active session", () => {
-    const selectedSession = testSession();
-    const active = createAppActions(createContext({ selectedSession }).context);
-    const archived = createAppActions(createContext({ selectedSession: { ...selectedSession, archived: true } }).context);
-
-    expect(active.find((action) => action.id === "session.archive")?.enabled).toBe(true);
-    expect(archived.find((action) => action.id === "session.archive")?.enabled).toBe(false);
-  });
-
-  it("runs archive on the selected session", () => {
-    const { context, calls } = createContext({ selectedSession: testSession() });
-    const action = createAppActions(context).find((candidate) => candidate.id === "session.archive");
-
-    if (action !== undefined) void action.run();
-
-    expect(calls).toEqual(["archiveSession"]);
-  });
-
-  it("only enables stop while a session is actively working", () => {
-    const selectedSession = testSession();
-    const inactive = createAppActions(createContext({ selectedSession }).context);
-    const active = createAppActions(createContext({ selectedSession, status: testStatus({ isStreaming: true }) }).context);
-
-    expect(inactive.find((action) => action.id === "session.stop")?.enabled).toBe(false);
-    expect(active.find((action) => action.id === "session.stop")?.enabled).toBe(true);
-  });
-});
-
-function testWorkspace(): AppState["selectedWorkspace"] {
-  return { id: "w1", projectId: "p1", path: "/tmp/project", label: "main", isMain: true, isGitWorktree: false };
-}
-
-function testSession(): SessionInfo {
-  return { id: "s1", path: "/tmp/project/.pi/sessions/s1", cwd: "/tmp/project", created: "now", modified: "now", messageCount: 0, firstMessage: "" };
-}
-
-function testStatus(patch: Partial<NonNullable<AppState["status"]>> = {}): AppState["status"] {
-  return {
-    sessionId: "s1",
-    isStreaming: false,
-    isCompacting: false,
-    isBashRunning: false,
-    pendingMessageCount: 0,
-    tokens: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
-    cost: 0,
-    ...patch,
-  };
-}
diff --git a/src/client/src/appState.ts b/src/client/src/appState.ts
index d1df640..4052f04 100644
--- a/src/client/src/appState.ts
+++ b/src/client/src/appState.ts
@@ -1,5 +1,6 @@
 import type { CommandResult, FileContentResponse, FileTreeEntry, GitDiffResponse, GitStatusResponse, Project, SessionActivity, SessionInfo, SessionStatus, Workspace } from "./api";
 import type { ChatLine } from "./components/shared";
+import type { QualifiedContributionId } from "./plugins/types";
 
 export interface AppState {
   projects: Project[];
@@ -19,8 +20,8 @@ export interface AppState {
   commandDialog: Extract<CommandResult, { type: "select" }> | undefined;
   actionPaletteOpen: boolean;
   projectDialogOpen: boolean;
-  workspaceTool: "files" | "git";
-  mainView: "chat" | "files" | "git";
+  workspaceTool: QualifiedContributionId;
+  mainView: "chat" | QualifiedContributionId;
   fileTree: FileTreeEntry[];
   expandedDirs: Record<string, FileTreeEntry[]>;
   selectedFilePath: string | undefined;
@@ -53,7 +54,7 @@ export function initialAppState(): AppState {
     commandDialog: undefined,
     actionPaletteOpen: false,
     projectDialogOpen: false,
-    workspaceTool: "files",
+    workspaceTool: "core:workspace.files",
     mainView: "chat",
     fileTree: [],
     expandedDirs: {},
diff --git a/src/client/src/components/PiWebApp.ts b/src/client/src/components/PiWebApp.ts
index f6d1b58..35b8fed 100644
--- a/src/client/src/components/PiWebApp.ts
+++ b/src/client/src/components/PiWebApp.ts
@@ -2,7 +2,6 @@ import { LitElement, html } from "lit";
 import { customElement, query, state } from "lit/decorators.js";
 import type { Project, SessionInfo, Workspace } from "../api";
 import type { AppAction } from "../actions";
-import { createAppActions } from "../appActions";
 import { initialAppState, type AppState } from "../appState";
 import { FileExplorerController } from "../controllers/fileExplorerController";
 import { GitController } from "../controllers/gitController";
@@ -10,6 +9,10 @@ import { ProjectController } from "../controllers/projectController";
 import { SessionController } from "../controllers/sessionController";
 import { WorkspaceController } from "../controllers/workspaceController";
 import { KeyboardShortcutDispatcher } from "../keyboardShortcuts";
+import type { QualifiedContributionId, PluginRuntimeContext } from "../plugins/types";
+import { corePlugin } from "../plugins/core";
+import { examplePlugin } from "../plugins/example";
+import { PluginRegistry } from "../plugins/registry";
 import { readRoute, writeRoute } from "../route";
 import "./ProjectList";
 import "./WorkspaceList";
@@ -58,6 +61,7 @@ export class PiWebApp extends LitElement {
     () => { this.updateUrl(); },
   );
   private readonly keyboard = new KeyboardShortcutDispatcher();
+  private readonly plugins = createPluginRegistry();
   private readonly onPopState = () => void this.withChatScrollTransition(() => this.restoreRoute(false));
   private readonly onKeyDown = (event: KeyboardEvent) => {
     if (this.keyboard.handle(event, this.getActions())) {
@@ -102,9 +106,9 @@ export class PiWebApp extends LitElement {
     const project = this.state.projects.find((p) => p.id === route.projectId);
     if (!project) return;
     await this.workspaces.selectProject(project, { workspaceId: route.workspaceId, sessionId: route.sessionId, updateUrl });
-    if (route.tool === "files") await this.files.refreshFiles();
+    if (route.tool === "core:workspace.files") await this.files.refreshFiles();
     if (route.file !== undefined) await this.files.selectFile(route.file);
-    if (route.tool === "git") await this.git.refreshGit();
+    if (route.tool === "core:workspace.git") await this.git.refreshGit();
     if (route.diff !== undefined) await this.git.selectDiff(route.diff);
     this.git.updatePolling();
   }
@@ -140,26 +144,23 @@ export class PiWebApp extends LitElement {
     });
   }
 
-  private selectWorkspaceTool(tool: "files" | "git") {
+  private selectWorkspaceTool(tool: QualifiedContributionId) {
     this.setState({ workspaceTool: tool, mainView: tool });
     this.updateUrl();
-    if (tool === "files") void this.files.refreshFiles();
-    else void this.git.refreshGit();
+    this.refreshSelectedWorkspaceTool(tool);
     this.git.updatePolling();
   }
 
-  private selectMainView(view: "chat" | "files" | "git") {
+  private selectMainView(view: AppState["mainView"]) {
     this.setState({ mainView: view, workspaceTool: view === "chat" ? this.state.workspaceTool : view });
     this.updateUrl();
-    if (view === "files") void this.files.refreshFiles();
-    if (view === "git") void this.git.refreshGit();
+    if (view !== "chat") this.refreshSelectedWorkspaceTool(view);
     this.git.updatePolling();
   }
 
   private handleWorkspaceChange(previous: AppState, next: AppState) {
     if (previous.selectedWorkspace?.id === next.selectedWorkspace?.id || next.selectedWorkspace === undefined) return;
-    if (next.workspaceTool === "files") void this.files.refreshFiles();
-    if (next.workspaceTool === "git") void this.git.refreshGit();
+    this.refreshSelectedWorkspaceTool(next.workspaceTool);
     this.git.updatePolling();
   }
 
@@ -168,28 +169,37 @@ export class PiWebApp extends LitElement {
     const nowActive = isActive(next.status);
     if (wasActive && !nowActive) {
       this.setState({ fileTreeStale: true, gitStale: true });
-      if (this.state.workspaceTool === "files") void this.files.refreshFiles();
-      if (this.state.workspaceTool === "git") void this.git.refreshGit();
+      this.refreshSelectedWorkspaceTool(this.state.workspaceTool);
     }
   }
 
+  private refreshSelectedWorkspaceTool(tool: QualifiedContributionId): void {
+    if (tool === "core:workspace.files") void this.files.refreshFiles();
+    if (tool === "core:workspace.git") void this.git.refreshGit();
+  }
+
   private renderWorkspacePanel() {
-    return html`<workspace-panel .workspace=${this.state.selectedWorkspace} .tool=${this.state.workspaceTool} .fileTree=${this.state.fileTree} .expandedDirs=${this.state.expandedDirs} .selectedFilePath=${this.state.selectedFilePath} .selectedFileContent=${this.state.selectedFileContent} .fileTreeStale=${this.state.fileTreeStale} .gitStatus=${this.state.gitStatus} .selectedDiffPath=${this.state.selectedDiffPath} .selectedDiff=${this.state.selectedDiff} .selectedStagedDiff=${this.state.selectedStagedDiff} .gitStale=${this.state.gitStale} .onSelectTool=${(tool: "files" | "git") => { this.selectWorkspaceTool(tool); }} .onRefreshFiles=${() => this.files.refreshFiles()} .onExpandDir=${(path: string) => this.files.expandDir(path)} .onSelectFile=${(path: string) => this.files.selectFile(path)} .onRefreshGit=${() => this.git.refreshGit()} .onSelectDiff=${(path: string) => this.git.selectDiff(path)}></workspace-panel>`;
+    return html`<workspace-panel .workspace=${this.state.selectedWorkspace} .tool=${this.state.workspaceTool} .panels=${this.plugins.getWorkspacePanels()} .fileTree=${this.state.fileTree} .expandedDirs=${this.state.expandedDirs} .selectedFilePath=${this.state.selectedFilePath} .selectedFileContent=${this.state.selectedFileContent} .fileTreeStale=${this.state.fileTreeStale} .gitStatus=${this.state.gitStatus} .selectedDiffPath=${this.state.selectedDiffPath} .selectedDiff=${this.state.selectedDiff} .selectedStagedDiff=${this.state.selectedStagedDiff} .gitStale=${this.state.gitStale} .onSelectTool=${(tool: QualifiedContributionId) => { this.selectWorkspaceTool(tool); }} .onRefreshFiles=${() => this.files.refreshFiles()} .onExpandDir=${(path: string) => this.files.expandDir(path)} .onSelectFile=${(path: string) => this.files.selectFile(path)} .onRefreshGit=${() => this.git.refreshGit()} .onSelectDiff=${(path: string) => this.git.selectDiff(path)}></workspace-panel>`;
   }
 
   private getActions(): AppAction[] {
-    return createAppActions({
+    return this.plugins.getActions(this.createPluginRuntimeContext());
+  }
+
+  private createPluginRuntimeContext(): PluginRuntimeContext {
+    return {
       state: this.state,
       openActionPalette: () => { this.setState({ actionPaletteOpen: true }); },
       focusPrompt: () => { this.promptEditor?.focusInput(); },
       addProject: () => { this.setState({ projectDialogOpen: true }); },
       selectMainView: (view) => { this.selectMainView(view); },
+      selectWorkspaceTool: (tool) => { this.selectWorkspaceTool(tool); },
       refreshFiles: () => this.files.refreshFiles(),
       refreshGit: () => this.git.refreshGit(),
       startSession: () => this.withChatScrollTransition(() => this.sessions.startSession()),
       archiveSession: () => this.sessions.archiveSession(),
       stopActiveWork: () => this.sessions.stopActiveWork(),
-    });
+    };
   }
 
   private runAction(actionId: string) {
@@ -210,11 +220,12 @@ export class PiWebApp extends LitElement {
           <workspace-list .workspaces=${state.workspaces} .selected=${state.selectedWorkspace} .onSelect=${(workspace: Workspace) => this.withChatScrollTransition(() => this.workspaces.selectWorkspace(workspace))}></workspace-list>
           <session-list .sessions=${state.sessions} .statuses=${state.sessionStatuses} .activities=${state.sessionActivities} .selected=${state.selectedSession} .canStart=${!!state.selectedWorkspace} .onStart=${() => this.withChatScrollTransition(() => this.sessions.startSession())} .onSelect=${(session: SessionInfo) => this.withChatScrollTransition(() => this.sessions.selectSession(session))} .onArchive=${(session: SessionInfo) => this.sessions.archiveSession(session)} .onRestore=${(session: SessionInfo) => this.sessions.restoreSession(session)}></session-list>
         </aside>
-        <main class=${`${state.mainView}-view`}>
+        <main class=${state.mainView === "chat" ? "chat-view" : "workspace-view"}>
           <div class="mobile-tabs">
             <button class=${state.mainView === "chat" ? "selected" : ""} @click=${() => { this.selectMainView("chat"); }}>Chat</button>
-            <button class=${state.mainView === "files" ? "selected" : ""} @click=${() => { this.selectMainView("files"); }}>Files</button>
-            <button class=${state.mainView === "git" ? "selected" : ""} @click=${() => { this.selectMainView("git"); }}>Git</button>
+            ${this.plugins.getWorkspacePanels().map((panel) => html`
+              <button class=${state.mainView === panel.id ? "selected" : ""} @click=${() => { this.selectMainView(panel.id); }}>${panel.title}</button>
+            `)}
           </div>
           ${state.error ? html`<div class="error">${state.error}</div>` : null}
           ${state.selectedSession ? html`
@@ -235,6 +246,13 @@ export class PiWebApp extends LitElement {
   static override styles = appStyles;
 }
 
+function createPluginRegistry(): PluginRegistry {
+  const registry = new PluginRegistry();
+  registry.register(corePlugin);
+  registry.register(examplePlugin);
+  return registry;
+}
+
 function isActive(status: AppState["status"]): boolean {
   return status?.isStreaming === true || status?.isBashRunning === true || status?.isCompacting === true;
 }
diff --git a/src/client/src/components/WorkspacePanel.ts b/src/client/src/components/WorkspacePanel.ts
index 86250c2..030cdd7 100644
--- a/src/client/src/components/WorkspacePanel.ts
+++ b/src/client/src/components/WorkspacePanel.ts
@@ -1,13 +1,14 @@
-import { LitElement, html, type TemplateResult } from "lit";
+import { LitElement, html } from "lit";
 import { customElement, property } from "lit/decorators.js";
 import type { FileContentResponse, FileTreeEntry, GitDiffResponse, GitStatusResponse, Workspace } from "../api";
+import type { QualifiedContributionId, QualifiedWorkspacePanelContribution, WorkspacePanelContext } from "../plugins/types";
 import { workspacePanelStyles } from "./shared";
-import "./CodeViewer";
 
 @customElement("workspace-panel")
 export class WorkspacePanel extends LitElement {
   @property({ attribute: false }) workspace: Workspace | undefined;
-  @property() tool: "files" | "git" = "files";
+  @property() tool: QualifiedContributionId = "core:workspace.files";
+  @property({ attribute: false }) panels: QualifiedWorkspacePanelContribution[] = [];
   @property({ attribute: false }) fileTree: FileTreeEntry[] = [];
   @property({ attribute: false }) expandedDirs: Record<string, FileTreeEntry[]> = {};
   @property({ attribute: false }) selectedFilePath: string | undefined;
@@ -18,7 +19,7 @@ export class WorkspacePanel extends LitElement {
   @property({ attribute: false }) selectedDiff: GitDiffResponse | undefined;
   @property({ attribute: false }) selectedStagedDiff: GitDiffResponse | undefined;
   @property({ type: Boolean }) gitStale = false;
-  @property({ attribute: false }) onSelectTool: (tool: "files" | "git") => void = () => undefined;
+  @property({ attribute: false }) onSelectTool: (tool: QualifiedContributionId) => void = () => undefined;
   @property({ attribute: false }) onRefreshFiles: () => void = () => undefined;
   @property({ attribute: false }) onExpandDir: (path: string) => void = () => undefined;
   @property({ attribute: false }) onSelectFile: (path: string) => void = () => undefined;
@@ -27,125 +28,40 @@ export class WorkspacePanel extends LitElement {
 
   override render() {
     if (!this.workspace) return html`<section class="empty">Select a workspace.</section>`;
+    const selectedPanel = this.panels.find((panel) => panel.id === this.tool) ?? this.panels[0];
     return html`
       <header>
         <div class="tabs">
-          <button class=${this.tool === "files" ? "selected" : ""} @click=${() => { this.onSelectTool("files"); }}>Files</button>
-          <button class=${this.tool === "git" ? "selected" : ""} @click=${() => { this.onSelectTool("git"); }}>Git</button>
+          ${this.panels.map((panel) => html`
+            <button class=${selectedPanel?.id === panel.id ? "selected" : ""} @click=${() => { this.onSelectTool(panel.id); }}>${panel.title}</button>
+          `)}
         </div>
         <small title=${this.workspace.path}>${this.workspace.label}</small>
       </header>
-      ${this.tool === "files" ? this.renderFiles() : this.renderGit()}
+      ${selectedPanel === undefined ? html`<section class="empty">No workspace panels registered.</section>` : selectedPanel.render(this.createPanelContext(this.workspace))}
     `;
   }
 
-  private renderFiles() {
-    return html`
-      <section class="toolbar">
-        <strong>Files</strong>
-        ${this.fileTreeStale ? html`<span class="stale">stale</span>` : null}
-        <button @click=${this.onRefreshFiles}>Refresh</button>
-      </section>
-      <section class="split">
-        <div class="list tree">
-          ${this.fileTree.length === 0 ? html`<p class="muted">No files loaded.</p>` : this.fileTree.map((entry) => this.renderTreeEntry(entry, 0))}
-        </div>
-        <div class="viewer">
-          ${this.renderFileViewer()}
-        </div>
-      </section>
-    `;
-  }
-
-  private renderTreeEntry(entry: FileTreeEntry, depth: number): TemplateResult {
-    const children = this.expandedDirs[entry.path];
-    const hasChildren = children !== undefined;
-    return html`
-      <button class="row" style=${`--depth:${String(depth)}`} @click=${() => { this.selectTreeEntry(entry); }}>
-        <span>${entry.type === "directory" ? (hasChildren ? "▾" : "▸") : "·"}</span>
-        <span>${entry.name}</span>
-      </button>
-      ${hasChildren ? children.map((child) => this.renderTreeEntry(child, depth + 1)) : null}
-    `;
-  }
-
-  private selectTreeEntry(entry: FileTreeEntry): void {
-    if (entry.type === "directory") this.onExpandDir(entry.path);
-    else this.onSelectFile(entry.path);
-  }
-
-  private renderFileViewer() {
-    const file = this.selectedFileContent;
-    if (this.selectedFilePath === undefined || this.selectedFilePath === "") return html`<p class="muted">Select a file.</p>`;
-    if (file === undefined) return html`<p class="muted">Loading ${this.selectedFilePath}…</p>`;
-    if (file.binary) return html`<p class="muted">Binary file: ${file.path}</p>`;
-    return html`
-      <div class="viewer-header"><strong>${file.path}</strong><small>${file.language ?? "text"}${file.truncated ? " · truncated" : ""}</small></div>
-      <code-viewer .content=${file.content} .language=${file.language}></code-viewer>
-    `;
-  }
-
-  private renderGit() {
-    const status = this.gitStatus;
-    return html`
-      <section class="toolbar">
-        <strong>Git</strong>
-        ${this.gitStale ? html`<span class="stale">stale</span>` : null}
-        <button @click=${this.onRefreshGit}>Refresh</button>
-      </section>
-      <section class="split">
-        <div class="list">
-          ${status === undefined ? html`<p class="muted">No status loaded.</p>` : !status.isGitRepo ? html`<p class="muted">Not a git repository.</p>` : html`
-            <p class="summary">${this.gitSummary(status)}</p>
-            ${status.files.length === 0 ? html`<p class="muted">No changes.</p>` : status.files.map((file) => html`
-              <button class="row ${this.selectedDiffPath === file.path ? "selected" : ""}" @click=${() => { this.onSelectDiff(file.path); }}>
-                <span>${stateLabel(file.index, file.workingTree)}</span>
-                <span>${file.path}</span>
-              </button>
-            `)}
-          `}
-        </div>
-        <div class="viewer">
-          ${this.renderDiffViewer()}
-        </div>
-      </section>
-    `;
-  }
-
-  private renderDiffViewer() {
-    if (this.selectedDiffPath === undefined || this.selectedDiffPath === "") return html`<p class="muted">Select a changed file.</p>`;
-    const unstaged = this.selectedDiff;
-    const staged = this.selectedStagedDiff;
-    if (unstaged === undefined || staged === undefined) return html`<p class="muted">Loading diff…</p>`;
-    const diffs = [staged, unstaged].filter((diff) => diff.diff !== "");
-    if (diffs.length === 0) return html`<p class="muted">No staged or unstaged diff.</p>`;
-    return html`
-      <div class=${diffs.length === 1 ? "diffs single" : "diffs"}>
-        ${diffs.map((diff) => this.renderDiffSection(diff))}
-      </div>
-    `;
-  }
-
-  private renderDiffSection(diff: GitDiffResponse) {
-    return html`
-      <section class="diff-section">
-        <div class="viewer-header"><strong>${diff.path ?? "diff"}</strong><small>${diff.staged ? "staged" : "unstaged"}${diff.truncated ? " · truncated" : ""}</small></div>
-        <code-viewer .content=${diff.diff} .language=${"diff"}></code-viewer>
-      </section>
-    `;
-  }
-
-  private gitSummary(status: GitStatusResponse): string {
-    const branch = status.branch ?? "detached";
-    const ahead = status.ahead ?? 0;
-    const behind = status.behind ?? 0;
-    return ahead === 0 && behind === 0 ? branch : `${branch} · ↑${String(ahead)} ↓${String(behind)}`;
+  private createPanelContext(workspace: Workspace): WorkspacePanelContext {
+    return {
+      workspace,
+      fileTree: this.fileTree,
+      expandedDirs: this.expandedDirs,
+      selectedFilePath: this.selectedFilePath,
+      selectedFileContent: this.selectedFileContent,
+      fileTreeStale: this.fileTreeStale,
+      gitStatus: this.gitStatus,
+      selectedDiffPath: this.selectedDiffPath,
+      selectedDiff: this.selectedDiff,
+      selectedStagedDiff: this.selectedStagedDiff,
+      gitStale: this.gitStale,
+      onRefreshFiles: this.onRefreshFiles,
+      onExpandDir: this.onExpandDir,
+      onSelectFile: this.onSelectFile,
+      onRefreshGit: this.onRefreshGit,
+      onSelectDiff: this.onSelectDiff,
+    };
   }
 
   static override styles = workspacePanelStyles;
 }
-
-function stateLabel(index: string, workingTree: string): string {
-  const label = workingTree !== "unmodified" ? workingTree : index;
-  return label.slice(0, 1).toUpperCase();
-}
diff --git a/src/client/src/components/shared.ts b/src/client/src/components/shared.ts
index f779f4e..b7e04e0 100644
--- a/src/client/src/components/shared.ts
+++ b/src/client/src/components/shared.ts
@@ -40,9 +40,8 @@ export const appStyles = css`
     .shell { grid-template-columns: 340px minmax(0, 1fr); }
     .shell > workspace-panel { display: none; }
     .mobile-tabs { display: flex; }
-    main.files-view chat-view, main.files-view prompt-editor, main.files-view status-bar,
-    main.git-view chat-view, main.git-view prompt-editor, main.git-view status-bar,
-    main.files-view .empty, main.git-view .empty { display: none; }
+    main.workspace-view chat-view, main.workspace-view prompt-editor, main.workspace-view status-bar,
+    main.workspace-view .empty { display: none; }
     main.chat-view .mobile-panel { display: none; }
     .mobile-panel { flex: 1 1 auto; min-height: 0; display: flex; }
     .mobile-panel workspace-panel { flex: 1 1 auto; border-left: 0; }
diff --git a/src/client/src/controllers/fileExplorerController.ts b/src/client/src/controllers/fileExplorerController.ts
index 555d902..5967233 100644
--- a/src/client/src/controllers/fileExplorerController.ts
+++ b/src/client/src/controllers/fileExplorerController.ts
@@ -38,7 +38,7 @@ export class FileExplorerController {
     const project = this.getState().selectedProject;
     const workspace = this.getState().selectedWorkspace;
     if (project === undefined || workspace === undefined) return;
-    this.setState({ selectedFilePath: path, selectedFileContent: undefined, workspaceTool: "files", mainView: this.getState().mainView === "chat" ? "chat" : "files" });
+    this.setState({ selectedFilePath: path, selectedFileContent: undefined, workspaceTool: "core:workspace.files", mainView: this.getState().mainView === "chat" ? "chat" : "core:workspace.files" });
     this.updateUrl();
     try {
       this.setState({ selectedFileContent: await api.workspaceFile(project.id, workspace.id, path), error: "" });
diff --git a/src/client/src/controllers/gitController.ts b/src/client/src/controllers/gitController.ts
index 708d51f..4c0712e 100644
--- a/src/client/src/controllers/gitController.ts
+++ b/src/client/src/controllers/gitController.ts
@@ -32,7 +32,7 @@ export class GitController {
   }
 
   async selectDiff(path: string): Promise<void> {
-    this.setState({ selectedDiffPath: path, selectedDiff: undefined, selectedStagedDiff: undefined, workspaceTool: "git", mainView: this.getState().mainView === "chat" ? "chat" : "git" });
+    this.setState({ selectedDiffPath: path, selectedDiff: undefined, selectedStagedDiff: undefined, workspaceTool: "core:workspace.git", mainView: this.getState().mainView === "chat" ? "chat" : "core:workspace.git" });
     this.updateUrl();
     await this.refreshDiff(path);
   }
@@ -55,7 +55,7 @@ export class GitController {
   updatePolling(): void {
     this.dispose();
     const state = this.getState();
-    if (state.workspaceTool === "git" || state.mainView === "git") {
+    if (state.workspaceTool === "core:workspace.git" || state.mainView === "core:workspace.git") {
       this.pollTimer = window.setInterval(() => { void this.refreshGit(); }, 8000);
     }
   }
diff --git a/src/client/src/appActions.ts b/src/client/src/plugins/core/actions.ts
similarity index 56%
rename from src/client/src/appActions.ts
rename to src/client/src/plugins/core/actions.ts
index 56aadd0..d550557 100644
--- a/src/client/src/appActions.ts
+++ b/src/client/src/plugins/core/actions.ts
@@ -1,24 +1,7 @@
-import type { AppAction } from "./actions";
-import type { AppState } from "./appState";
+import type { AppState } from "../../appState";
+import type { PluginAction } from "../types";
 
-export interface AppActionContext {
-  state: AppState;
-  openActionPalette: () => void;
-  focusPrompt: () => void;
-  addProject: () => void | Promise<void>;
-  selectMainView: (view: AppState["mainView"]) => void;
-  refreshFiles: () => void | Promise<void>;
-  refreshGit: () => void | Promise<void>;
-  startSession: () => void | Promise<void>;
-  archiveSession: () => void | Promise<void>;
-  stopActiveWork: () => void | Promise<void>;
-}
-
-export function createAppActions(context: AppActionContext): AppAction[] {
-  const hasWorkspace = context.state.selectedWorkspace !== undefined;
-  const hasSession = context.state.selectedSession !== undefined;
-  const canArchiveSession = hasSession && context.state.selectedSession?.archived !== true;
-  const isBusy = isActive(context.state.status);
+export function createCoreActions(): PluginAction[] {
   return [
     {
       id: "actions.show",
@@ -26,28 +9,28 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       description: "Open the command palette",
       shortcut: "mod+k",
       group: "General",
-      run: context.openActionPalette,
+      run: (context) => { context.openActionPalette(); },
     },
     {
       id: "prompt.focus",
       title: "Focus Prompt",
       description: "Move keyboard focus to the message composer",
       group: "General",
-      enabled: hasSession,
-      run: context.focusPrompt,
+      enabled: (context) => context.state.selectedSession !== undefined,
+      run: (context) => { context.focusPrompt(); },
     },
     {
       id: "project.add",
       title: "Add Project",
       group: "Project",
-      run: context.addProject,
+      run: (context) => context.addProject(),
     },
     {
       id: "view.chat",
       title: "Go to Chat",
       shortcut: "mod+1",
       group: "Navigation",
-      run: () => { context.selectMainView("chat"); },
+      run: (context) => { context.selectMainView("chat"); },
     },
     {
       id: "view.files",
@@ -55,7 +38,7 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       shortcut: "mod+2",
       group: "Navigation",
       enabled: hasWorkspace,
-      run: () => { context.selectMainView("files"); },
+      run: (context) => { context.selectMainView("core:workspace.files"); },
     },
     {
       id: "view.git",
@@ -63,7 +46,7 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       shortcut: "mod+3",
       group: "Navigation",
       enabled: hasWorkspace,
-      run: () => { context.selectMainView("git"); },
+      run: (context) => { context.selectMainView("core:workspace.git"); },
     },
     {
       id: "workspace.refresh-files",
@@ -71,7 +54,7 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       shortcut: "mod+shift+f",
       group: "Workspace",
       enabled: hasWorkspace,
-      run: context.refreshFiles,
+      run: (context) => context.refreshFiles(),
     },
     {
       id: "workspace.refresh-git",
@@ -79,7 +62,7 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       shortcut: "mod+shift+g",
       group: "Workspace",
       enabled: hasWorkspace,
-      run: context.refreshGit,
+      run: (context) => context.refreshGit(),
     },
     {
       id: "workspace.refresh-current",
@@ -87,7 +70,7 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       shortcut: "mod+shift+r",
       group: "Workspace",
       enabled: hasWorkspace,
-      run: () => context.state.workspaceTool === "git" ? context.refreshGit() : context.refreshFiles(),
+      run: (context) => context.state.workspaceTool === "core:workspace.git" ? context.refreshGit() : context.refreshFiles(),
     },
     {
       id: "session.start",
@@ -95,27 +78,31 @@ export function createAppActions(context: AppActionContext): AppAction[] {
       shortcut: "mod+enter",
       group: "Session",
       enabled: hasWorkspace,
-      run: context.startSession,
+      run: (context) => context.startSession(),
     },
     {
       id: "session.archive",
       title: "Archive Session",
       description: "Archive the selected session",
       group: "Session",
-      enabled: canArchiveSession,
-      run: context.archiveSession,
+      enabled: (context) => context.state.selectedSession !== undefined && context.state.selectedSession.archived !== true,
+      run: (context) => context.archiveSession(),
     },
     {
       id: "session.stop",
       title: "Stop Active Work",
       shortcut: "mod+.",
       group: "Session",
-      enabled: hasSession && isBusy,
-      run: context.stopActiveWork,
+      enabled: (context) => context.state.selectedSession !== undefined && isActive(context.state.status),
+      run: (context) => context.stopActiveWork(),
     },
   ];
 }
 
+function hasWorkspace(context: { state: AppState }): boolean {
+  return context.state.selectedWorkspace !== undefined;
+}
+
 function isActive(status: AppState["status"]): boolean {
   return status?.isStreaming === true || status?.isBashRunning === true || status?.isCompacting === true;
 }
diff --git a/src/client/src/plugins/core/index.ts b/src/client/src/plugins/core/index.ts
new file mode 100644
index 0000000..5fbdb47
--- /dev/null
+++ b/src/client/src/plugins/core/index.ts
@@ -0,0 +1,12 @@
+import type { PiWebPlugin } from "../types";
+import { createCoreActions } from "./actions";
+import { createCoreWorkspacePanels } from "./panels";
+
+export const corePlugin: PiWebPlugin = {
+  id: "core",
+  name: "Pi Web Core",
+  activate: () => ({
+    actions: createCoreActions(),
+    workspacePanels: createCoreWorkspacePanels(),
+  }),
+};
diff --git a/src/client/src/plugins/core/panels.ts b/src/client/src/plugins/core/panels.ts
new file mode 100644
index 0000000..2e21f52
--- /dev/null
+++ b/src/client/src/plugins/core/panels.ts
@@ -0,0 +1,129 @@
+import { html, type TemplateResult } from "lit";
+import type { FileTreeEntry, GitDiffResponse, GitStatusResponse } from "../../api";
+import type { WorkspacePanelContribution, WorkspacePanelContext } from "../types";
+import "../../components/CodeViewer";
+
+export function createCoreWorkspacePanels(): WorkspacePanelContribution[] {
+  return [
+    {
+      id: "workspace.files",
+      title: "Files",
+      order: 10,
+      render: renderFiles,
+    },
+    {
+      id: "workspace.git",
+      title: "Git",
+      order: 20,
+      render: renderGit,
+    },
+  ];
+}
+
+function renderFiles(context: WorkspacePanelContext): TemplateResult {
+  return html`
+    <section class="toolbar">
+      <strong>Files</strong>
+      ${context.fileTreeStale ? html`<span class="stale">stale</span>` : null}
+      <button @click=${context.onRefreshFiles}>Refresh</button>
+    </section>
+    <section class="split">
+      <div class="list tree">
+        ${context.fileTree.length === 0 ? html`<p class="muted">No files loaded.</p>` : context.fileTree.map((entry) => renderTreeEntry(context, entry, 0))}
+      </div>
+      <div class="viewer">
+        ${renderFileViewer(context)}
+      </div>
+    </section>
+  `;
+}
+
+function renderTreeEntry(context: WorkspacePanelContext, entry: FileTreeEntry, depth: number): TemplateResult {
+  const children = context.expandedDirs[entry.path];
+  const hasChildren = children !== undefined;
+  return html`
+    <button class="row" style=${`--depth:${String(depth)}`} @click=${() => { selectTreeEntry(context, entry); }}>
+      <span>${entry.type === "directory" ? (hasChildren ? "▾" : "▸") : "·"}</span>
+      <span>${entry.name}</span>
+    </button>
+    ${hasChildren ? children.map((child) => renderTreeEntry(context, child, depth + 1)) : null}
+  `;
+}
+
+function selectTreeEntry(context: WorkspacePanelContext, entry: FileTreeEntry): void {
+  if (entry.type === "directory") context.onExpandDir(entry.path);
+  else context.onSelectFile(entry.path);
+}
+
+function renderFileViewer(context: WorkspacePanelContext): TemplateResult {
+  const file = context.selectedFileContent;
+  if (context.selectedFilePath === undefined || context.selectedFilePath === "") return html`<p class="muted">Select a file.</p>`;
+  if (file === undefined) return html`<p class="muted">Loading ${context.selectedFilePath}…</p>`;
+  if (file.binary) return html`<p class="muted">Binary file: ${file.path}</p>`;
+  return html`
+    <div class="viewer-header"><strong>${file.path}</strong><small>${file.language ?? "text"}${file.truncated ? " · truncated" : ""}</small></div>
+    <code-viewer .content=${file.content} .language=${file.language}></code-viewer>
+  `;
+}
+
+function renderGit(context: WorkspacePanelContext): TemplateResult {
+  const status = context.gitStatus;
+  return html`
+    <section class="toolbar">
+      <strong>Git</strong>
+      ${context.gitStale ? html`<span class="stale">stale</span>` : null}
+      <button @click=${context.onRefreshGit}>Refresh</button>
+    </section>
+    <section class="split">
+      <div class="list">
+        ${status === undefined ? html`<p class="muted">No status loaded.</p>` : !status.isGitRepo ? html`<p class="muted">Not a git repository.</p>` : html`
+          <p class="summary">${gitSummary(status)}</p>
+          ${status.files.length === 0 ? html`<p class="muted">No changes.</p>` : status.files.map((file) => html`
+            <button class="row ${context.selectedDiffPath === file.path ? "selected" : ""}" @click=${() => { context.onSelectDiff(file.path); }}>
+              <span>${stateLabel(file.index, file.workingTree)}</span>
+              <span>${file.path}</span>
+            </button>
+          `)}
+        `}
+      </div>
+      <div class="viewer">
+        ${renderDiffViewer(context)}
+      </div>
+    </section>
+  `;
+}
+
+function renderDiffViewer(context: WorkspacePanelContext): TemplateResult {
+  if (context.selectedDiffPath === undefined || context.selectedDiffPath === "") return html`<p class="muted">Select a changed file.</p>`;
+  const unstaged = context.selectedDiff;
+  const staged = context.selectedStagedDiff;
+  if (unstaged === undefined || staged === undefined) return html`<p class="muted">Loading diff…</p>`;
+  const diffs = [staged, unstaged].filter((diff) => diff.diff !== "");
+  if (diffs.length === 0) return html`<p class="muted">No staged or unstaged diff.</p>`;
+  return html`
+    <div class=${diffs.length === 1 ? "diffs single" : "diffs"}>
+      ${diffs.map((diff) => renderDiffSection(diff))}
+    </div>
+  `;
+}
+
+function renderDiffSection(diff: GitDiffResponse): TemplateResult {
+  return html`
+    <section class="diff-section">
+      <div class="viewer-header"><strong>${diff.path ?? "diff"}</strong><small>${diff.staged ? "staged" : "unstaged"}${diff.truncated ? " · truncated" : ""}</small></div>
+      <code-viewer .content=${diff.diff} .language=${"diff"}></code-viewer>
+    </section>
+  `;
+}
+
+function gitSummary(status: GitStatusResponse): string {
+  const branch = status.branch ?? "detached";
+  const ahead = status.ahead ?? 0;
+  const behind = status.behind ?? 0;
+  return ahead === 0 && behind === 0 ? branch : `${branch} · ↑${String(ahead)} ↓${String(behind)}`;
+}
+
+function stateLabel(index: string, workingTree: string): string {
+  const label = workingTree !== "unmodified" ? workingTree : index;
+  return label.slice(0, 1).toUpperCase();
+}
diff --git a/src/client/src/plugins/example/index.ts b/src/client/src/plugins/example/index.ts
new file mode 100644
index 0000000..04f8030
--- /dev/null
+++ b/src/client/src/plugins/example/index.ts
@@ -0,0 +1,36 @@
+import { html } from "lit";
+import type { PiWebPlugin } from "../types";
+
+export const examplePlugin: PiWebPlugin = {
+  id: "example",
+  name: "Example Plugin",
+  activate: () => ({
+    actions: [
+      {
+        id: "workspace.show-path",
+        title: "Show Current Workspace Path",
+        group: "Example",
+        enabled: (context) => context.state.selectedWorkspace !== undefined,
+        run: (context) => {
+          const path = context.state.selectedWorkspace?.path ?? "No workspace selected";
+          window.alert(path);
+        },
+      },
+    ],
+    workspacePanels: [
+      {
+        id: "workspace.info",
+        title: "Info",
+        order: 100,
+        render: (context) => html`
+          <section class="toolbar"><strong>Info</strong></section>
+          <section class="viewer">
+            <p><strong>Workspace</strong></p>
+            <p class="muted">${context.workspace.label}</p>
+            <p class="muted">${context.workspace.path}</p>
+          </section>
+        `,
+      },
+    ],
+  }),
+};
diff --git a/src/client/src/plugins/registry.test.ts b/src/client/src/plugins/registry.test.ts
new file mode 100644
index 0000000..f25d211
--- /dev/null
+++ b/src/client/src/plugins/registry.test.ts
@@ -0,0 +1,79 @@
+import { describe, expect, it, vi } from "vitest";
+import { initialAppState, type AppState } from "../appState";
+import { corePlugin } from "./core";
+import { PluginRegistry } from "./registry";
+import type { PluginRuntimeContext } from "./types";
+
+function createContext(statePatch: Partial<AppState> = {}) {
+  const calls: string[] = [];
+  const context: PluginRuntimeContext = {
+    state: { ...initialAppState(), ...statePatch },
+    openActionPalette: vi.fn(() => { calls.push("openActionPalette"); }),
+    focusPrompt: vi.fn(() => { calls.push("focusPrompt"); }),
+    addProject: vi.fn(() => { calls.push("addProject"); }),
+    selectMainView: vi.fn((view: AppState["mainView"]) => { calls.push(`selectMainView:${view}`); }),
+    selectWorkspaceTool: vi.fn((tool: AppState["workspaceTool"]) => { calls.push(`selectWorkspaceTool:${tool}`); }),
+    refreshFiles: vi.fn(() => { calls.push("refreshFiles"); }),
+    refreshGit: vi.fn(() => { calls.push("refreshGit"); }),
+    startSession: vi.fn(() => { calls.push("startSession"); }),
+    archiveSession: vi.fn(() => { calls.push("archiveSession"); }),
+    stopActiveWork: vi.fn(() => { calls.push("stopActiveWork"); }),
+  };
+  return { context, calls };
+}
+
+describe("PluginRegistry", () => {
+  it("namespaces contribution ids with the owning plugin id", () => {
+    const registry = new PluginRegistry();
+    registry.register(corePlugin);
+
+    expect(registry.getActions(createContext().context).some((action) => action.id === "core:actions.show")).toBe(true);
+    expect(registry.getWorkspacePanels().map((panel) => panel.id)).toEqual(["core:workspace.files", "core:workspace.git"]);
+  });
+
+  it("rejects duplicate ids within the same namespace", () => {
+    const registry = new PluginRegistry();
+
+    expect(() => {
+      registry.register({
+        id: "example",
+        name: "Example",
+        activate: () => ({
+          actions: [
+            { id: "duplicate", title: "One", run: () => undefined },
+            { id: "duplicate", title: "Two", run: () => undefined },
+          ],
+        }),
+      });
+    }).toThrow("Duplicate contribution id: example:duplicate");
+  });
+
+  it("evaluates core action enablement against runtime state", () => {
+    const registry = new PluginRegistry();
+    registry.register(corePlugin);
+
+    const inactive = registry.getActions(createContext().context);
+    const active = registry.getActions(createContext({ selectedWorkspace: testWorkspace() }).context);
+
+    expect(inactive.find((action) => action.id === "core:view.files")?.enabled).toBe(false);
+    expect(active.find((action) => action.id === "core:view.files")?.enabled).toBe(true);
+  });
+
+  it("routes refresh current to the active core workspace panel", () => {
+    const registry = new PluginRegistry();
+    registry.register(corePlugin);
+    const { context, calls } = createContext({
+      selectedWorkspace: testWorkspace(),
+      workspaceTool: "core:workspace.git",
+    });
+    const action = registry.getActions(context).find((candidate) => candidate.id === "core:workspace.refresh-current");
+
+    if (action !== undefined) void action.run();
+
+    expect(calls).toEqual(["refreshGit"]);
+  });
+});
+
+function testWorkspace(): AppState["selectedWorkspace"] {
+  return { id: "w1", projectId: "p1", path: "/tmp/project", label: "main", isMain: true, isGitWorktree: false };
+}
diff --git a/src/client/src/plugins/registry.ts b/src/client/src/plugins/registry.ts
new file mode 100644
index 0000000..56020d5
--- /dev/null
+++ b/src/client/src/plugins/registry.ts
@@ -0,0 +1,75 @@
+import type { PiWebPlugin, PluginAction, PluginRuntimeContext, QualifiedContributionId, QualifiedPluginAction, QualifiedWorkspacePanelContribution, WorkspacePanelContribution } from "./types";
+
+const idPattern = /^[a-z][a-z0-9.-]*$/u;
+const localIdPattern = /^[a-z][a-z0-9.-]*$/u;
+
+type RegisteredPluginAction = Omit<PluginAction, "id"> & {
+  id: QualifiedContributionId;
+  pluginId: string;
+  localId: string;
+};
+
+export class PluginRegistry {
+  private readonly actions: RegisteredPluginAction[] = [];
+  private readonly workspacePanels: QualifiedWorkspacePanelContribution[] = [];
+  private readonly pluginIds = new Set<string>();
+  private readonly contributionIds = new Set<QualifiedContributionId>();
+
+  register(plugin: PiWebPlugin): void {
+    this.validatePluginId(plugin.id);
+    if (this.pluginIds.has(plugin.id)) throw new Error(`Duplicate plugin id: ${plugin.id}`);
+    this.pluginIds.add(plugin.id);
+
+    const contributions = plugin.activate({ apiVersion: 1 });
+    for (const action of contributions.actions ?? []) this.actions.push(this.qualifyAction(plugin.id, action));
+    for (const panel of contributions.workspacePanels ?? []) this.workspacePanels.push(this.qualifyWorkspacePanel(plugin.id, panel));
+  }
+
+  getActions(context: PluginRuntimeContext): QualifiedPluginAction[] {
+    return this.actions.map((action) => {
+      const enabled = typeof action.enabled === "function" ? action.enabled(context) : action.enabled;
+      const qualified: QualifiedPluginAction = {
+        id: action.id,
+        pluginId: action.pluginId,
+        localId: action.localId,
+        title: action.title,
+        run: () => action.run(context),
+      };
+      if (action.description !== undefined) qualified.description = action.description;
+      if (action.shortcut !== undefined) qualified.shortcut = action.shortcut;
+      if (action.group !== undefined) qualified.group = action.group;
+      if (enabled !== undefined) qualified.enabled = enabled;
+      return qualified;
+    });
+  }
+
+  getWorkspacePanels(): QualifiedWorkspacePanelContribution[] {
+    return [...this.workspacePanels].sort((left, right) => (left.order ?? 1000) - (right.order ?? 1000) || left.title.localeCompare(right.title));
+  }
+
+  private qualifyAction(pluginId: string, action: PluginAction): RegisteredPluginAction {
+    const id = this.qualify(pluginId, action.id);
+    return { ...action, id, pluginId, localId: action.id };
+  }
+
+  private qualifyWorkspacePanel(pluginId: string, panel: WorkspacePanelContribution): QualifiedWorkspacePanelContribution {
+    const id = this.qualify(pluginId, panel.id);
+    return { ...panel, id, pluginId, localId: panel.id };
+  }
+
+  private qualify(pluginId: string, localId: string): QualifiedContributionId {
+    this.validateLocalId(localId);
+    const qualified: QualifiedContributionId = `${pluginId}:${localId}`;
+    if (this.contributionIds.has(qualified)) throw new Error(`Duplicate contribution id: ${qualified}`);
+    this.contributionIds.add(qualified);
+    return qualified;
+  }
+
+  private validatePluginId(pluginId: string): void {
+    if (!idPattern.test(pluginId)) throw new Error(`Invalid plugin id: ${pluginId}`);
+  }
+
+  private validateLocalId(localId: string): void {
+    if (!localIdPattern.test(localId)) throw new Error(`Invalid contribution id: ${localId}`);
+  }
+}
diff --git a/src/client/src/plugins/types.ts b/src/client/src/plugins/types.ts
new file mode 100644
index 0000000..c3e54bb
--- /dev/null
+++ b/src/client/src/plugins/types.ts
@@ -0,0 +1,84 @@
+import type { TemplateResult } from "lit";
+import type { AppAction } from "../actions";
+import type { FileContentResponse, FileTreeEntry, GitDiffResponse, GitStatusResponse, Workspace } from "../api";
+import type { AppState } from "../appState";
+
+export type PluginId = string;
+export type LocalContributionId = string;
+export type QualifiedContributionId = `${PluginId}:${LocalContributionId}`;
+
+export interface PiWebPlugin {
+  id: PluginId;
+  name: string;
+  activate: (context: PluginActivationContext) => PluginContributions;
+}
+
+export interface PluginActivationContext {
+  apiVersion: 1;
+}
+
+export interface PluginContributions {
+  actions?: PluginAction[];
+  workspacePanels?: WorkspacePanelContribution[];
+}
+
+export interface PluginRuntimeContext {
+  state: AppState;
+  openActionPalette: () => void;
+  focusPrompt: () => void;
+  addProject: () => void | Promise<void>;
+  selectMainView: (view: AppState["mainView"]) => void;
+  selectWorkspaceTool: (tool: QualifiedContributionId) => void;
+  refreshFiles: () => void | Promise<void>;
+  refreshGit: () => void | Promise<void>;
+  startSession: () => void | Promise<void>;
+  archiveSession: () => void | Promise<void>;
+  stopActiveWork: () => void | Promise<void>;
+}
+
+export interface PluginAction {
+  id: LocalContributionId;
+  title: string;
+  description?: string;
+  shortcut?: string;
+  group?: string;
+  enabled?: boolean | ((context: PluginRuntimeContext) => boolean);
+  run: (context: PluginRuntimeContext) => void | Promise<void>;
+}
+
+export interface QualifiedPluginAction extends AppAction {
+  pluginId: PluginId;
+  localId: LocalContributionId;
+}
+
+export interface WorkspacePanelContext {
+  workspace: Workspace;
+  fileTree: FileTreeEntry[];
+  expandedDirs: Record<string, FileTreeEntry[]>;
+  selectedFilePath: string | undefined;
+  selectedFileContent: FileContentResponse | undefined;
+  fileTreeStale: boolean;
+  gitStatus: GitStatusResponse | undefined;
+  selectedDiffPath: string | undefined;
+  selectedDiff: GitDiffResponse | undefined;
+  selectedStagedDiff: GitDiffResponse | undefined;
+  gitStale: boolean;
+  onRefreshFiles: () => void;
+  onExpandDir: (path: string) => void;
+  onSelectFile: (path: string) => void;
+  onRefreshGit: () => void;
+  onSelectDiff: (path: string) => void;
+}
+
+export interface WorkspacePanelContribution {
+  id: LocalContributionId;
+  title: string;
+  order?: number;
+  render: (context: WorkspacePanelContext) => TemplateResult;
+}
+
+export interface QualifiedWorkspacePanelContribution extends WorkspacePanelContribution {
+  id: QualifiedContributionId;
+  pluginId: PluginId;
+  localId: LocalContributionId;
+}
diff --git a/src/client/src/route.test.ts b/src/client/src/route.test.ts
index cb0eb1f..c02bebf 100644
--- a/src/client/src/route.test.ts
+++ b/src/client/src/route.test.ts
@@ -36,8 +36,8 @@ describe("route helpers", () => {
       projectId: "p1",
       workspaceId: "w1",
       sessionId: "s1",
-      tool: "git",
-      view: "files",
+      tool: "core:workspace.git",
+      view: "core:workspace.files",
       file: "src/main.ts",
       diff: "README.md",
     });
@@ -55,7 +55,7 @@ describe("route helpers", () => {
       projectId: "project/id",
       workspaceId: "workspace id",
       sessionId: "",
-      tool: "files",
+      tool: "core:workspace.files",
       view: "chat",
       file: "src/main.ts",
       diff: undefined,
@@ -63,13 +63,13 @@ describe("route helpers", () => {
 
     writeRoute(route);
 
-    expect(pushed).toEqual(["http://localhost/app?old=1&project=project%2Fid&workspace=workspace+id&tool=files&view=chat&file=src%2Fmain.ts#section"]);
+    expect(pushed).toEqual(["http://localhost/app?old=1&project=project%2Fid&workspace=workspace+id&tool=core%3Aworkspace.files&view=chat&file=src%2Fmain.ts#section"]);
   });
 
   it("does not push history when the route is unchanged", () => {
-    const { pushed } = installWindow("http://localhost/app?project=p1&tool=git");
+    const { pushed } = installWindow("http://localhost/app?project=p1&tool=core%3Aworkspace.git");
 
-    writeRoute({ projectId: "p1", workspaceId: undefined, sessionId: undefined, tool: "git", view: undefined, file: undefined, diff: undefined });
+    writeRoute({ projectId: "p1", workspaceId: undefined, sessionId: undefined, tool: "core:workspace.git", view: undefined, file: undefined, diff: undefined });
 
     expect(pushed).toEqual([]);
   });
diff --git a/src/client/src/route.ts b/src/client/src/route.ts
index aa4213e..84e325c 100644
--- a/src/client/src/route.ts
+++ b/src/client/src/route.ts
@@ -1,9 +1,11 @@
+import type { QualifiedContributionId } from "./plugins/types";
+
 export interface AppRoute {
   projectId: string | undefined;
   workspaceId: string | undefined;
   sessionId: string | undefined;
-  tool: "files" | "git" | undefined;
-  view: "chat" | "files" | "git" | undefined;
+  tool: QualifiedContributionId | undefined;
+  view: "chat" | QualifiedContributionId | undefined;
   file: string | undefined;
   diff: string | undefined;
 }
@@ -42,10 +44,19 @@ export function writeRoute(route: AppRoute): void {
   if (next !== current) window.history.pushState({}, "", url);
 }
 
-function parseTool(value: string | null): "files" | "git" | undefined {
-  return value === "files" || value === "git" ? value : undefined;
+function parseTool(value: string | null): QualifiedContributionId | undefined {
+  if (value === "files") return "core:workspace.files";
+  if (value === "git") return "core:workspace.git";
+  return isQualifiedId(value) ? value : undefined;
 }
 
-function parseView(value: string | null): "chat" | "files" | "git" | undefined {
-  return value === "chat" || value === "files" || value === "git" ? value : undefined;
+function parseView(value: string | null): "chat" | QualifiedContributionId | undefined {
+  if (value === "chat") return "chat";
+  if (value === "files") return "core:workspace.files";
+  if (value === "git") return "core:workspace.git";
+  return isQualifiedId(value) ? value : undefined;
+}
+
+function isQualifiedId(value: string | null): value is QualifiedContributionId {
+  return value !== null && /^[a-z][a-z0-9.-]*:[a-z][a-z0-9.-]*$/u.test(value);
 }