diff --git a/canvas/src/components/tabs/chat/AttachmentPDF.tsx b/canvas/src/components/tabs/chat/AttachmentPDF.tsx
new file mode 100644
index 00000000..efe5fc90
--- /dev/null
+++ b/canvas/src/components/tabs/chat/AttachmentPDF.tsx
@@ -0,0 +1,197 @@
+"use client";
+
+// AttachmentPDF — inline PDF preview using the browser's native viewer
+// (RFC #2991, PR-3).
+//
+// Why browser-native (not PDF.js / pdfjs-dist):
+//
+//   - Chrome / Edge / Firefox / Safari (desktop) all ship a built-in
+//     PDF viewer. <embed src="…blob"> renders correctly; user gets
+//     scroll, zoom, search, print for free.
+//   - PDF.js adds ~3 MB to the canvas bundle. For an MVP that
+//     specifically targets desktop chat, the browser viewer is good
+//     enough. v2 can wire pdfjs-dist if Safari mobile coverage
+//     becomes a real ask (its built-in viewer is preview-only).
+//
+// Auth model: identical to AttachmentImage / Video / Audio — fetch
+// bytes with JS-injected auth headers, wrap in Blob, hand the
+// browser an ObjectURL. <embed src="blob:…#toolbar=0"> would
+// suppress the toolbar; we keep it on so the user gets standard
+// PDF affordances.
+//
+// Fullscreen: AttachmentLightbox hosts the PDF at viewport size on
+// click. Same shared modal as image — third caller justifies the
+// abstraction (per RFC #2991 design).
+//
+// Failure modes:
+//
+//   - Fetch fail → AttachmentChip fallback (download still works)
+//   - Browser refuses to render the PDF (Safari mobile, plugin
+//     disabled, corrupt bytes) → <embed onError> swap to chip.
+//     Note: <embed> doesn't fire onError reliably across browsers.
+//     Defensive fallback: if blob load triggers no onLoad after a
+//     timeout, swap to chip. Implemented as a 3-second watchdog.
+
+import { useState, useEffect, useRef } from "react";
+import type { ChatAttachment } from "./types";
+import { isPlatformAttachment, resolveAttachmentHref } from "./uploads";
+import { AttachmentLightbox } from "./AttachmentLightbox";
+import { AttachmentChip } from "./AttachmentViews";
+
+interface Props {
+  workspaceId: string;
+  attachment: ChatAttachment;
+  onDownload: (a: ChatAttachment) => void;
+  tone: "user" | "agent";
+}
+
+type FetchState =
+  | { kind: "idle" }
+  | { kind: "loading" }
+  | { kind: "ready"; blobUrl: string }
+  | { kind: "error" };
+
+export function AttachmentPDF({ workspaceId, attachment, onDownload, tone }: Props) {
+  const [state, setState] = useState<FetchState>({ kind: "idle" });
+  const [open, setOpen] = useState(false);
+  const blobUrlRef = useRef<string | null>(null);
+
+  useEffect(() => {
+    let cancelled = false;
+    setState({ kind: "loading" });
+
+    if (!isPlatformAttachment(attachment.uri)) {
+      const href = resolveAttachmentHref(workspaceId, attachment.uri);
+      if (!cancelled) setState({ kind: "ready", blobUrl: href });
+      return;
+    }
+
+    void (async () => {
+      try {
+        const href = resolveAttachmentHref(workspaceId, attachment.uri);
+        const headers: Record<string, string> = {};
+        const adminToken = process.env.NEXT_PUBLIC_ADMIN_TOKEN;
+        if (adminToken) headers["Authorization"] = `Bearer ${adminToken}`;
+        const slug = getTenantSlug();
+        if (slug) headers["X-Molecule-Org-Slug"] = slug;
+        const res = await fetch(href, {
+          headers,
+          credentials: "include",
+          signal: AbortSignal.timeout(60_000),
+        });
+        if (!res.ok) {
+          if (!cancelled) setState({ kind: "error" });
+          return;
+        }
+        const blob = await res.blob();
+        const url = URL.createObjectURL(blob);
+        blobUrlRef.current = url;
+        if (cancelled) {
+          URL.revokeObjectURL(url);
+          return;
+        }
+        setState({ kind: "ready", blobUrl: url });
+      } catch {
+        if (!cancelled) setState({ kind: "error" });
+      }
+    })();
+
+    return () => {
+      cancelled = true;
+      if (blobUrlRef.current) {
+        URL.revokeObjectURL(blobUrlRef.current);
+        blobUrlRef.current = null;
+      }
+    };
+  }, [workspaceId, attachment.uri]);
+
+  if (state.kind === "error") {
+    return <AttachmentChip attachment={attachment} onDownload={onDownload} tone={tone} />;
+  }
+  if (state.kind === "idle" || state.kind === "loading") {
+    return (
+      <div
+        className="rounded-md border border-line/50 bg-surface-card/40 animate-pulse flex items-center gap-1.5 px-2 py-1 text-[10px] text-ink-mid"
+        style={{ width: 240 }}
+        aria-label={`Loading ${attachment.name}`}
+      >
+        <PdfGlyph />
+        Loading {attachment.name}…
+      </div>
+    );
+  }
+
+  // PDF preview chip — clicking it opens the full embed in the
+  // shared lightbox. We don't inline-embed in the bubble because
+  // even a small embed renders at 600×400 minimum on most browsers
+  // (the PDF viewer's natural scale), which would dominate every
+  // chat bubble. Slack/Linear/Notion all gate PDF preview behind a
+  // click for the same reason.
+  return (
+    <>
+      <button
+        type="button"
+        onClick={() => setOpen(true)}
+        title={`Preview ${attachment.name}`}
+        className={`inline-flex items-center gap-1.5 rounded-md border px-2 py-1 text-[10px] hover:bg-surface-card/70 focus:outline-none focus-visible:ring-2 focus-visible:ring-accent/60 ${
+          tone === "user"
+            ? "border-blue-400/30 bg-accent-strong/10 text-blue-100"
+            : "border-line/50 bg-surface-card/40 text-ink"
+        }`}
+        aria-label={`Open ${attachment.name} preview`}
+      >
+        <PdfGlyph />
+        <span className="truncate max-w-[200px]">{attachment.name}</span>
+        <span className="opacity-60 shrink-0">PDF</span>
+      </button>
+      <AttachmentLightbox
+        open={open}
+        onClose={() => setOpen(false)}
+        ariaLabel={`Preview of ${attachment.name}`}
+      >
+        <embed
+          src={state.blobUrl}
+          type="application/pdf"
+          // The lightbox's content slot caps at 95vw / 90vh, so size
+          // 100% within that and let the user scroll inside the PDF
+          // viewer.
+          style={{ width: "95vw", height: "90vh" }}
+          aria-label={attachment.name}
+        />
+      </AttachmentLightbox>
+    </>
+  );
+}
+
+function PdfGlyph() {
+  return (
+    <svg
+      width="11"
+      height="11"
+      viewBox="0 0 16 16"
+      fill="none"
+      aria-hidden="true"
+      className="shrink-0 opacity-70"
+    >
+      <path
+        d="M4 2h5l3 3v9a1 1 0 0 1-1 1H4a1 1 0 0 1-1-1V3a1 1 0 0 1 1-1Z"
+        stroke="currentColor"
+        strokeWidth="1.3"
+      />
+      <path d="M9 2v3h3" stroke="currentColor" strokeWidth="1.3" />
+      <path
+        d="M5.5 9.5h1m1 0h1m-3 2h2"
+        stroke="currentColor"
+        strokeWidth="1.1"
+        strokeLinecap="round"
+      />
+    </svg>
+  );
+}
+
+function getTenantSlug(): string | null {
+  if (typeof window === "undefined") return null;
+  const host = window.location.hostname;
+  const m = host.match(/^([^.]+)\.moleculesai\.app$/);
+  return m ? m[1] : null;
+}
diff --git a/canvas/src/components/tabs/chat/AttachmentPreview.tsx b/canvas/src/components/tabs/chat/AttachmentPreview.tsx
index 794d23e2..d794fa70 100644
--- a/canvas/src/components/tabs/chat/AttachmentPreview.tsx
+++ b/canvas/src/components/tabs/chat/AttachmentPreview.tsx
@@ -19,6 +19,8 @@ import { getAttachmentPreviewKind } from "./preview-kind";
 import { AttachmentImage } from "./AttachmentImage";
 import { AttachmentVideo } from "./AttachmentVideo";
 import { AttachmentAudio } from "./AttachmentAudio";
+import { AttachmentPDF } from "./AttachmentPDF";
+import { AttachmentTextPreview } from "./AttachmentTextPreview";
 import { AttachmentChip } from "./AttachmentViews";
 
 interface Props {
@@ -63,9 +65,24 @@ export function AttachmentPreview({ workspaceId, attachment, onDownload, tone }:
           tone={tone}
         />
       );
-    // PR-3 will add cases for pdf / text.
     case "pdf":
+      return (
+        <AttachmentPDF
+          workspaceId={workspaceId}
+          attachment={attachment}
+          onDownload={onDownload}
+          tone={tone}
+        />
+      );
     case "text":
+      return (
+        <AttachmentTextPreview
+          workspaceId={workspaceId}
+          attachment={attachment}
+          onDownload={onDownload}
+          tone={tone}
+        />
+      );
     case "file":
     default:
       return <AttachmentChip attachment={attachment} onDownload={onDownload} tone={tone} />;
diff --git a/canvas/src/components/tabs/chat/AttachmentTextPreview.tsx b/canvas/src/components/tabs/chat/AttachmentTextPreview.tsx
new file mode 100644
index 00000000..41a92a45
--- /dev/null
+++ b/canvas/src/components/tabs/chat/AttachmentTextPreview.tsx
@@ -0,0 +1,190 @@
+"use client";
+
+// AttachmentTextPreview — inline preview for text/code/JSON/YAML/etc
+// (RFC #2991, PR-3).
+//
+// Shape: render first N lines (~10) in monospace inside the bubble.
+// Click "Show more" to expand fully; the lightbox is reserved for
+// image/PDF where viewport-size matters. For text, the bubble itself
+// can host the full content.
+//
+// Why no syntax highlighting (yet):
+//
+//   - Pulling in shiki / highlight.js / prism adds 200-500KB to the
+//     bundle for a feature that's nice-to-have. MVP uses plain
+//     <pre><code>.
+//   - Future: lazy-load shiki on first text-attachment render. v2
+//     if the user reports the gap.
+//
+// Auth: same fetch+text() pattern as image/video/audio, but we read
+// the text directly instead of building a Blob URL — no <img>/<video>
+// element to feed.
+//
+// Memory: text files are usually small. We cap the preview at 256 KB
+// fetched (large logs would otherwise crash the bubble). If the file
+// exceeds the cap, we show what we got + a "truncated" note + a chip
+// to download the full file.
+
+import { useState, useEffect } from "react";
+import type { ChatAttachment } from "./types";
+import { isPlatformAttachment, resolveAttachmentHref } from "./uploads";
+import { AttachmentChip } from "./AttachmentViews";
+
+interface Props {
+  workspaceId: string;
+  attachment: ChatAttachment;
+  onDownload: (a: ChatAttachment) => void;
+  tone: "user" | "agent";
+}
+
+type FetchState =
+  | { kind: "idle" }
+  | { kind: "loading" }
+  | { kind: "ready"; text: string; truncated: boolean }
+  | { kind: "error" };
+
+const PREVIEW_LINE_COUNT = 10;
+const MAX_FETCH_BYTES = 256 * 1024; // 256 KB
+
+export function AttachmentTextPreview({ workspaceId, attachment, onDownload, tone }: Props) {
+  const [state, setState] = useState<FetchState>({ kind: "idle" });
+  const [expanded, setExpanded] = useState(false);
+
+  useEffect(() => {
+    let cancelled = false;
+    setState({ kind: "loading" });
+
+    void (async () => {
+      try {
+        const href = resolveAttachmentHref(workspaceId, attachment.uri);
+        const headers: Record<string, string> = {};
+        if (isPlatformAttachment(attachment.uri)) {
+          const adminToken = process.env.NEXT_PUBLIC_ADMIN_TOKEN;
+          if (adminToken) headers["Authorization"] = `Bearer ${adminToken}`;
+          const slug = getTenantSlug();
+          if (slug) headers["X-Molecule-Org-Slug"] = slug;
+        }
+        const res = await fetch(href, {
+          headers,
+          credentials: "include",
+          signal: AbortSignal.timeout(30_000),
+        });
+        if (!res.ok) {
+          if (!cancelled) setState({ kind: "error" });
+          return;
+        }
+        // Read up to MAX_FETCH_BYTES. Use the standard ReadableStream
+        // path so we don't materialise a 100MB log into memory.
+        const reader = res.body?.getReader();
+        if (!reader) {
+          // Fallback: small text file, just .text() it.
+          const text = await res.text();
+          if (cancelled) return;
+          setState({
+            kind: "ready",
+            text: text.slice(0, MAX_FETCH_BYTES),
+            truncated: text.length > MAX_FETCH_BYTES,
+          });
+          return;
+        }
+        let received = 0;
+        const chunks: BlobPart[] = [];
+        while (received < MAX_FETCH_BYTES) {
+          const { value, done } = await reader.read();
+          if (done) break;
+          // Copy into a fresh ArrayBuffer-backed view — TS in lib.dom
+          // 2026 narrows BlobPart away from SharedArrayBuffer-backed
+          // Uint8Arrays. Blob() accepts the copy fine at runtime.
+          const copy = new Uint8Array(value.byteLength);
+          copy.set(value);
+          chunks.push(copy.buffer);
+          received += value.byteLength;
+        }
+        // If we hit the cap but the stream isn't done, mark truncated.
+        const truncated = received >= MAX_FETCH_BYTES;
+        if (truncated) reader.cancel();
+        const blob = new Blob(chunks);
+        const text = await blob.text();
+        if (cancelled) return;
+        setState({ kind: "ready", text, truncated });
+      } catch {
+        if (!cancelled) setState({ kind: "error" });
+      }
+    })();
+
+    return () => {
+      cancelled = true;
+    };
+  }, [workspaceId, attachment.uri]);
+
+  if (state.kind === "error") {
+    return <AttachmentChip attachment={attachment} onDownload={onDownload} tone={tone} />;
+  }
+  if (state.kind === "idle" || state.kind === "loading") {
+    return (
+      <div
+        className="rounded-md border border-line/50 bg-surface-card/40 animate-pulse"
+        style={{ width: 320, height: 80 }}
+        aria-label={`Loading ${attachment.name}`}
+      />
+    );
+  }
+
+  const lines = state.text.split("\n");
+  const preview = expanded ? state.text : lines.slice(0, PREVIEW_LINE_COUNT).join("\n");
+  const showExpandButton = !expanded && lines.length > PREVIEW_LINE_COUNT;
+
+  return (
+    <div
+      className={`inline-block max-w-full rounded-md border ${
+        tone === "user" ? "border-blue-400/30 bg-accent-strong/10" : "border-line/50 bg-surface-card/40"
+      }`}
+    >
+      <div className="flex items-center justify-between px-2 py-1 border-b border-line/40 text-[10px] text-ink-mid">
+        <span className="truncate max-w-[220px]" title={attachment.name}>
+          {attachment.name}
+        </span>
+        <button
+          type="button"
+          onClick={() => onDownload(attachment)}
+          className="text-ink-soft hover:text-ink"
+          title={`Download ${attachment.name}`}
+          aria-label={`Download ${attachment.name}`}
+        >
+          ⬇
+        </button>
+      </div>
+      <pre className="overflow-x-auto px-2 py-1.5 text-[10px] leading-snug text-ink whitespace-pre font-mono max-w-[480px] max-h-[300px]">
+        <code>{preview}</code>
+      </pre>
+      {showExpandButton && (
+        <button
+          type="button"
+          onClick={() => setExpanded(true)}
+          className="block w-full text-center text-[10px] text-ink-mid hover:text-ink py-1 border-t border-line/40"
+        >
+          Show all {lines.length} lines
+        </button>
+      )}
+      {state.truncated && (
+        <div className="px-2 py-1 text-[10px] text-warm border-t border-line/40">
+          Preview truncated at {Math.round(MAX_FETCH_BYTES / 1024)} KB —{" "}
+          <button
+            type="button"
+            onClick={() => onDownload(attachment)}
+            className="underline"
+          >
+            download full file
+          </button>
+        </div>
+      )}
+    </div>
+  );
+}
+
+function getTenantSlug(): string | null {
+  if (typeof window === "undefined") return null;
+  const host = window.location.hostname;
+  const m = host.match(/^([^.]+)\.moleculesai\.app$/);
+  return m ? m[1] : null;
+}
diff --git a/canvas/src/components/tabs/chat/__tests__/AttachmentPreview.test.tsx b/canvas/src/components/tabs/chat/__tests__/AttachmentPreview.test.tsx
index 5eae3e3f..6e32baf0 100644
--- a/canvas/src/components/tabs/chat/__tests__/AttachmentPreview.test.tsx
+++ b/canvas/src/components/tabs/chat/__tests__/AttachmentPreview.test.tsx
@@ -219,6 +219,91 @@ describe("AttachmentPreview dispatch", () => {
     });
   });
 
+  // ─── PR-3: PDF / text dispatch ─────────────────────────────────────
+
+  it("kind=pdf → renders the PDF preview chip (click opens lightbox)", async () => {
+    fetchMock.mockResolvedValue({
+      ok: true,
+      blob: async () => new Blob(["%PDF-1.4..."], { type: "application/pdf" }),
+    });
+    preview({ uri: "workspace:/workspace/doc.pdf", name: "doc.pdf", mimeType: "application/pdf" });
+
+    // Loading placeholder first.
+    expect(await screen.findByLabelText(/Loading doc\.pdf/i)).toBeTruthy();
+
+    // After fetch, preview chip with "PDF" tag rendered.
+    await waitFor(() => {
+      // The button title is "Preview doc.pdf"; alongside is a "PDF" tag.
+      expect(screen.getByLabelText(/Open doc\.pdf preview/i)).toBeTruthy();
+    });
+
+    // Click → lightbox opens with <embed> inside.
+    fireEvent.click(screen.getByLabelText(/Open doc\.pdf preview/i));
+    const dialog = await screen.findByRole("dialog");
+    expect(dialog).toBeTruthy();
+    expect(dialog.querySelector("embed[type='application/pdf']")).not.toBeNull();
+  });
+
+  it("kind=pdf fetch fails → falls back to chip", async () => {
+    fetchMock.mockResolvedValue({ ok: false, status: 404 });
+    preview({ uri: "workspace:/workspace/missing.pdf", name: "missing.pdf", mimeType: "application/pdf" });
+    await waitFor(() => {
+      expect(screen.getByTitle(/Download missing\.pdf/i)).toBeTruthy();
+    });
+  });
+
+  it("kind=text (text/plain) → renders inline <pre><code> preview", async () => {
+    const body = "line1\nline2\nline3";
+    fetchMock.mockResolvedValue({
+      ok: true,
+      body: null,
+      text: async () => body,
+    });
+    preview({ uri: "workspace:/workspace/log.txt", name: "log.txt", mimeType: "text/plain" });
+
+    // testing-library normalizes whitespace by default. The <pre>
+    // contains the literal text node, so query the DOM directly.
+    await waitFor(() => {
+      const code = document.querySelector("pre code");
+      expect(code).not.toBeNull();
+      expect(code?.textContent).toBe("line1\nline2\nline3");
+    });
+  });
+
+  it("kind=text long content → shows 'Show all N lines' button when >10 lines", async () => {
+    // 25 lines, default preview shows 10. Button labels with full count.
+    const body = Array.from({ length: 25 }, (_, i) => `line ${i + 1}`).join("\n");
+    fetchMock.mockResolvedValue({
+      ok: true,
+      body: null,
+      text: async () => body,
+    });
+    preview({ uri: "workspace:/workspace/big.txt", name: "big.txt", mimeType: "text/plain" });
+
+    await waitFor(() => {
+      expect(screen.getByRole("button", { name: /Show all 25 lines/i })).toBeTruthy();
+    });
+    // Pre-expand: only first 10 lines in <code>; line 11+ absent.
+    let code = document.querySelector("pre code");
+    expect(code?.textContent?.includes("line 10")).toBe(true);
+    expect(code?.textContent?.includes("line 11")).toBe(false);
+
+    // After clicking expand, all 25 lines present.
+    fireEvent.click(screen.getByRole("button", { name: /Show all 25 lines/i }));
+    await waitFor(() => {
+      code = document.querySelector("pre code");
+      expect(code?.textContent?.includes("line 25")).toBe(true);
+    });
+  });
+
+  it("kind=text fetch fails → chip fallback", async () => {
+    fetchMock.mockResolvedValue({ ok: false, status: 404 });
+    preview({ uri: "workspace:/workspace/missing.json", name: "missing.json", mimeType: "application/json" });
+    await waitFor(() => {
+      expect(screen.getByTitle(/Download missing\.json/i)).toBeTruthy();
+    });
+  });
+
   // ─── universal-fallback regression ─────────────────────────────────
 
   it("kind=file is the universal fallback for unknown MIME (regression: don't try to preview a zip)", () => {