diff --git a/apps/web/src/components/chat/chatCanvasLayout.test.ts b/apps/web/src/components/chat/chatCanvasLayout.test.ts
index 748d8abb5d1ac..c016861225e08 100644
--- a/apps/web/src/components/chat/chatCanvasLayout.test.ts
+++ b/apps/web/src/components/chat/chatCanvasLayout.test.ts
@@ -8,7 +8,7 @@ import {
 
 const preview: ChatCanvasPreview = {
   key: "browser:one",
-  width: 320,
+  width: null,
   position: null,
   source: { width: 1600, height: 1000 },
 };
@@ -64,13 +64,94 @@ describe("chat canvas layout", () => {
       }
     }
   });
+  it.each([
+    { canvasWidth: 744, previewWidth: 240 },
+    { canvasWidth: 900, previewWidth: null },
+    { canvasWidth: 900, previewWidth: 240 },
+    { canvasWidth: 952, previewWidth: 400 },
+  ])(
+    "keeps chat fixed with a $previewWidth preview in a compact $canvasWidth pixel canvas",
+    ({ canvasWidth, previewWidth }) => {
+      const original = resolve(canvasWidth, null).chat;
+      for (const x of [12, canvasWidth / 2, canvasWidth - 252]) {
+        const result = resolve(canvasWidth, {
+          ...preview,
+          width: previewWidth,
+          position: { x, y: 200 },
+          source: { width: 390, height: 844 },
+        });
+        expect(result.chat).toEqual(original);
+        expect(result.overlapsChat).toBe(true);
+      }
+    },
+  );
+
+  it("reflows chat once the canvas has room for the minimum side-by-side layout", () => {
+    const result = resolve(953, {
+      ...preview,
+      width: 240,
+      position: { x: 701, y: 200 },
+    });
+    expect(result.chat).toMatchObject({ left: 48, width: 641 });
+    expectClear(result);
+  });
+
+  it.each([1012, 1040, 1100])(
+    "overlays a preview when details already constrain chat in a %spx canvas",
+    (width) => {
+      const layout = (preview: ChatCanvasPreview | null) =>
+        resolveChatCanvasLayout({
+          container: { width, height: 900 },
+          maxChatWidth: 736,
+          composerHeight: 180,
+          detailsCard: { left: width - 292, right: width - 12, bottom: 400 },
+          preview,
+        });
+      const original = layout(null).chat;
+      for (const x of [12, width / 2, width - 412]) {
+        const result = layout({
+          ...preview,
+          width: 400,
+          position: { x, y: 200 },
+          source: { width: 768, height: 1024 },
+        });
+        expect(result.chat).toEqual(original);
+        expect(result.overlapsChat).toBe(true);
+      }
+    },
+  );
+
+  it("folds details around a manually dragged preview and expands them after moving away", () => {
+    const container = { width: 1584, height: 988 };
+    const detailsCard = { left: 1292, right: 1572, bottom: 400 };
+    const layout = (position: ChatCanvasPreview["position"]) =>
+      resolveChatCanvasLayout({
+        container,
+        detailsCard,
+        preview: { ...preview, width: null, position },
+      });
+    const density = (result: ReturnType<typeof layout>) => {
+      const card = resolveThreadDetailsCardLayout({
+        container,
+        lane: { padding: 48, minChatWidth: 640 },
+        frame: result.frame,
+        overlapsDetailsCard: result.overlapsDetailsCard,
+      })!;
+      return resolveThreadDetailsCardDensity(card.height, { full: 388, compact: 182 });
+    };
+    const dragged = layout({ x: 1252, y: 275 });
+    expect(dragged.frame).toEqual({ x: 1252, y: 275, width: 320, height: 200 });
+    expect(density(dragged)).toBe("compact");
+    expect(density(layout({ x: 1252, y: 500 }))).toBe("full");
+    expect(layout(null).overlapsDetailsCard).toBe(false);
+  });
+
   it("lifts a growing preview above the composer without snapping at the chat boundary", () => {
     let previous: ReturnType<typeof resolve> | undefined;
     for (let width = 480; width <= 1100; width++) {
       const result = resolve(1344, {
         ...preview,
         width,
-        lastInteraction: "resize",
         position: { x: 1332 - width, y: 888 - Math.round(width / 1.6) },
       });
       const frame = result.frame!;
@@ -94,13 +175,11 @@ describe("chat canvas layout", () => {
     const moved = resolve(width, {
       ...preview,
       position: { x: start.x - 300, y: start.y },
-      lastInteraction: "drag",
     });
     expect(moved.frame).toEqual({ ...start, x: start.x - 300 });
     const returned = resolve(width, {
       ...preview,
       position: { x: start.x, y: start.y },
-      lastInteraction: "drag",
     });
     expect(returned.frame).toEqual(start);
   });
@@ -128,7 +207,7 @@ describe("chat canvas layout", () => {
     expect(resolve(1800, player).chat.width).toBe(768);
     expect(player.width).toBe(480);
   });
-  it("constrains a dragged preview below the full top-right card instead of folding it", () => {
+  it("folds the top-right card when a dragged preview crosses it", () => {
     const result = resolveChatCanvasLayout({
       container: { width: 1584, height: 988 },
       maxChatWidth: 736,
@@ -141,8 +220,8 @@ describe("chat canvas layout", () => {
         position: { x: 1260, y: 240 },
       },
     });
-    expect(result.frame).toEqual({ x: 1260, y: 351, width: 240, height: 365 });
-    expect(result.overlapsDetailsCard).toBe(false);
+    expect(result.frame).toEqual({ x: 1260, y: 240, width: 240, height: 365 });
+    expect(result.overlapsDetailsCard).toBe(true);
     expect(result.chat).toEqual({ left: 424, width: 736, insetStart: 0, insetEnd: 0 });
   });
   it("moves the chat left only as far as a details card it would crowd requires", () => {
@@ -175,9 +254,9 @@ describe("chat canvas layout", () => {
       expect(Math.abs(leftAt(width + 1) - leftAt(width))).toBeLessThanOrEqual(1);
     }
   });
-  it("keeps a dragged or resized preview below the open find bar", () => {
+  it("keeps default-sized and explicitly sized previews below the open find bar", () => {
     const findBar = { left: 1292, right: 1572, bottom: 48 };
-    const layout = (lastInteraction: "drag" | "resize") =>
+    const layout = (width: number | null) =>
       resolveChatCanvasLayout({
         container: { width: 1584, height: 988 },
         maxChatWidth: 736,
@@ -185,20 +264,23 @@ describe("chat canvas layout", () => {
         findBar,
         preview: {
           ...preview,
-          width: 240,
+          width,
           source: { width: 240, height: 365 },
           position: { x: 1332, y: 12 },
-          lastInteraction,
         },
       });
-    for (const lastInteraction of ["drag", "resize"] as const) {
-      const result = layout(lastInteraction);
-      expect(result.frame).toEqual({ x: 1332, y: 60, width: 240, height: 365 });
+    for (const width of [null, 240]) {
+      const result = layout(width);
+      expect(result.frame).toEqual({
+        x: 1332,
+        y: 60,
+        ...(width === null ? { width: 210, height: 320 } : { width: 240, height: 365 }),
+      });
       expect(result.overlapsDetailsCard).toBe(false);
       expect(result.chat).toEqual({ left: 424, width: 736, insetStart: 0, insetEnd: 0 });
     }
   });
-  it("uses space beside the full card if a tall preview cannot fit below it", () => {
+  it("opens beside the full card if a tall preview cannot fit below it", () => {
     const result = resolveChatCanvasLayout({
       container: { width: 1584, height: 988 },
       maxChatWidth: 736,
@@ -208,14 +290,14 @@ describe("chat canvas layout", () => {
         ...preview,
         width: 240,
         source: { width: 240, height: 700 },
-        position: { x: 1260, y: 100 },
+        position: null,
       },
     });
-    expect(result.frame).toEqual({ x: 1008, y: 100, width: 240, height: 700 });
+    expect(result.frame).toEqual({ x: 1008, y: 276, width: 240, height: 700 });
     expect(result.overlapsDetailsCard).toBe(false);
     expectClear(result);
   });
-  it("keeps a large player when clearing the full card would leave no readable chat", () => {
+  it("preserves the chosen size while folding the card and keeping chat readable", () => {
     const container = { width: 1584, height: 988 };
     const source = { width: 1000, height: 1523 };
     const layout = (width: number) => {
@@ -237,13 +319,13 @@ describe("chat canvas layout", () => {
     const shifted = layout(460);
     expect(shifted.frame!.width).toBe(460);
     expect(shifted.chat.left).toBeLessThan(424);
-    expect(shifted.overlapsDetailsCard).toBe(false);
+    expect(shifted.overlapsDetailsCard).toBe(true);
     expectClear(shifted);
 
     const narrowed = layout(532);
     expect(narrowed.frame!.width).toBe(532);
-    expect(narrowed.chat.width).toBe(656);
-    expect(narrowed.overlapsDetailsCard).toBe(false);
+    expect(narrowed.chat.width).toBe(736);
+    expect(narrowed.overlapsDetailsCard).toBe(true);
     expectClear(narrowed);
 
     const grown = layout(600);
@@ -276,7 +358,6 @@ describe("chat canvas layout", () => {
             width: resized.width,
             position: resized,
             source,
-            lastInteraction: "resize",
           },
         });
       };
@@ -307,7 +388,7 @@ describe("chat canvas layout", () => {
       expect(density(layout(400))).toBe("full");
     },
   );
-  it("requests card folding only when no full-card slot fits and keeps the composer clear", () => {
+  it("folds details around an oversized preview while keeping the composer clear", () => {
     const result = resolveChatCanvasLayout({
       container: { width: 1584, height: 988 },
       maxChatWidth: 736,
@@ -317,7 +398,7 @@ describe("chat canvas layout", () => {
         ...preview,
         width: 1300,
         source: { width: 1300, height: 400 },
-        position: { x: 12, y: 12 },
+        position: { x: 12, y: 700 },
       },
     });
     expect(result.overlapsDetailsCard).toBe(true);
diff --git a/apps/web/src/components/chat/chatCanvasLayout.ts b/apps/web/src/components/chat/chatCanvasLayout.ts
index 77e276ee817f4..1be526a256145 100644
--- a/apps/web/src/components/chat/chatCanvasLayout.ts
+++ b/apps/web/src/components/chat/chatCanvasLayout.ts
@@ -1,5 +1,6 @@
 import {
   clampPreviewMiniPlayerPosition,
+  PREVIEW_MINI_PLAYER_MIN_SIZE,
   resolvePreviewMiniPlayerFrame,
   type PreviewMiniPlayerFrame,
   type PreviewMiniPlayerObstacles,
@@ -56,15 +57,20 @@ export function resolveChatCanvasLayout({
   let frame: PreviewMiniPlayerFrame | null = null;
   let overlapsChat = false;
   if (preview && container.width > 0 && container.height > 0) {
+    const explicitlySized = preview.width !== null;
+    const canReflowChat =
+      normalWidth === centeredWidth &&
+      container.width > padding + minChatWidth + PREVIEW_MINI_PLAYER_MIN_SIZE.width + GAP * 2;
     frame = resolvePreviewMiniPlayerFrame({ ...preview, container });
     // Reserve a chat lane only if the preview still has room to drag.
     const minimumPreviewX =
-      preview.lastInteraction === "resize" ||
+      explicitlySized ||
+      !canReflowChat ||
       container.width <= padding + minChatWidth + frame.width + GAP * 2
         ? GAP
         : padding + minChatWidth + GAP;
     if (preview.position === null) frame = { ...frame, y: container.height - frame.height - GAP };
-    if (preview.lastInteraction === "resize" && composerHeight > 0) {
+    if (explicitlySized && composerHeight > 0) {
       const laneWidth = Math.min(normalWidth, minChatWidth);
       const transitionWidth = Math.max(GAP, normalWidth - laneWidth);
       const lift = Math.min(
@@ -96,7 +102,7 @@ export function resolveChatCanvasLayout({
             bottom: Math.max(detailsCard.bottom, findBar.bottom),
           }
         : (detailsCard ?? findBar);
-    const cardObstacle = preview.lastInteraction === "resize" ? findBar : dragObstacle;
+    const cardObstacle = preview.position === null ? dragObstacle : findBar;
     frame = {
       ...frame,
       ...clampPreviewMiniPlayerPosition(
@@ -110,6 +116,7 @@ export function resolveChatCanvasLayout({
     const chatBeside = (player: PreviewMiniPlayerFrame) => {
       const normalRight = normalLeft + normalWidth;
       if (player.x >= normalRight + GAP) return chat;
+      if (!canReflowChat) return null;
       const width = Math.min(maxChatWidth, player.x - GAP - padding);
       if (width < minChatWidth) return null;
       const left = Math.min(normalLeft, player.x - GAP - width);
@@ -127,7 +134,7 @@ export function resolveChatCanvasLayout({
     }
     if (nextChat) chat = nextChat;
     else overlapsChat = true;
-    if (overlapsChat && preview.lastInteraction === "resize") {
+    if (overlapsChat && explicitlySized && canReflowChat) {
       const width = Math.min(normalWidth, minChatWidth);
       chat = {
         left: padding,
diff --git a/apps/web/src/components/preview/previewMiniPlayerLayout.test.ts b/apps/web/src/components/preview/previewMiniPlayerLayout.test.ts
index 4d9eff507ed37..5181d3d9d92b5 100644
--- a/apps/web/src/components/preview/previewMiniPlayerLayout.test.ts
+++ b/apps/web/src/components/preview/previewMiniPlayerLayout.test.ts
@@ -35,6 +35,57 @@ describe("resolvePreviewMiniPlayerSourceSize", () => {
 });
 
 describe("resolvePreviewMiniPlayerFrame", () => {
+  it("fits a portrait phone's default preview inside the default box", () => {
+    expect(
+      resolvePreviewMiniPlayerFrame({
+        width: null,
+        position: null,
+        source: { width: 390, height: 844 },
+        container,
+      }),
+    ).toMatchObject({ width: 148, height: 320 });
+  });
+
+  it.each([
+    { width: 390, height: 844 },
+    { width: 768, height: 1024 },
+    { width: 1024, height: 768 },
+  ])("lets a $width×$height device shrink below 240 pixels wide", (source) => {
+    const requestedWidth = source.width > source.height ? 210 : 140;
+    const expected = {
+      width: requestedWidth,
+      height: Math.round((requestedWidth * source.height) / source.width),
+    };
+    expect(
+      resolvePreviewMiniPlayerFrame({ width: requestedWidth, position: null, source, container }),
+    ).toMatchObject(expected);
+    expect(
+      resizePreviewMiniPlayer({
+        start: { x: 12, y: 12, width: 240, height: (240 * source.height) / source.width },
+        direction: "east",
+        delta: { x: requestedWidth - 240, y: 0 },
+        source,
+        container,
+      }),
+    ).toMatchObject(expected);
+  });
+
+  it.each([
+    { source, width: 240 },
+    { source: { width: 1600, height: 900 }, width: 267 },
+    { source: { width: 2100, height: 900 }, width: 350 },
+  ])("keeps wide previews at least 150 pixels tall", ({ source, width }) => {
+    expect(
+      resizePreviewMiniPlayer({
+        start: { x: 12, y: 12, width: 400, height: (400 * source.height) / source.width },
+        direction: "east",
+        delta: { x: -399, y: 0 },
+        source,
+        container,
+      }),
+    ).toMatchObject({ width, height: 150 });
+  });
+
   it("shrinks to the space above the composer without losing the stored width", () => {
     const frame = resolvePreviewMiniPlayerFrame({
       width: 800,
diff --git a/apps/web/src/components/preview/previewMiniPlayerLayout.ts b/apps/web/src/components/preview/previewMiniPlayerLayout.ts
index f66183c9fcb12..3675d568802f2 100644
--- a/apps/web/src/components/preview/previewMiniPlayerLayout.ts
+++ b/apps/web/src/components/preview/previewMiniPlayerLayout.ts
@@ -14,7 +14,7 @@ export const PREVIEW_MINI_PLAYER_CORNER_RADIUS = 12;
 // The mini-player shell straddles this webview at 47 and 49: above --z-sheet, under dialogs (50).
 export const PREVIEW_MINI_PLAYER_WEBVIEW_Z_INDEX = 48;
 const PREVIEW_MINI_PLAYER_DEFAULT_BOX = { width: 320, height: 320 } as const;
-const PREVIEW_MINI_PLAYER_MIN_SIZE = { width: 240, height: 150 } as const;
+export const PREVIEW_MINI_PLAYER_MIN_SIZE = { width: 240, height: 150 } as const;
 
 export interface PreviewMiniPlayerFrame extends PreviewMiniPlayerPosition, PreviewMiniPlayerSize {}
 
@@ -108,10 +108,7 @@ const availableArea = (
 });
 
 const minimumPreviewMiniPlayerWidth = (source: PreviewMiniPlayerSize) =>
-  Math.max(
-    PREVIEW_MINI_PLAYER_MIN_SIZE.width,
-    (PREVIEW_MINI_PLAYER_MIN_SIZE.height * source.width) / source.height,
-  );
+  (PREVIEW_MINI_PLAYER_MIN_SIZE.height * source.width) / source.height;
 
 function fitPreviewMiniPlayerWidth(
   desiredWidth: number,
diff --git a/apps/web/src/previewMiniPlayerStore.test.ts b/apps/web/src/previewMiniPlayerStore.test.ts
index 538fdc11e6602..66e891315b5b2 100644
--- a/apps/web/src/previewMiniPlayerStore.test.ts
+++ b/apps/web/src/previewMiniPlayerStore.test.ts
@@ -7,6 +7,11 @@ import {
   selectThreadPreviewMiniPlayer,
   usePreviewMiniPlayerStore,
 } from "./previewMiniPlayerStore";
+import { resolveChatCanvasLayout } from "./components/chat/chatCanvasLayout";
+import {
+  resolveThreadDetailsCardDensity,
+  resolveThreadDetailsCardLayout,
+} from "./components/chat/threadDetailsCardLayout";
 
 const refA = scopeThreadRef("env-1" as EnvironmentId, ThreadId.make("thread-A"));
 const tabA = browserMiniPlayerSource("tab-a");
@@ -17,6 +22,40 @@ beforeEach(() => {
 });
 
 describe("previewMiniPlayerStore", () => {
+  it("keeps a resized preview and folded details card in place when dragging starts", () => {
+    const store = usePreviewMiniPlayerStore.getState();
+    store.open(refA, tabA);
+    store.resize(refA, "browser:tab-a", 460, { x: 1112, y: 275 });
+    const container = { width: 1584, height: 988 };
+    const layout = () => {
+      const player = selectThreadPreviewMiniPlayer(
+        usePreviewMiniPlayerStore.getState().byThreadKey,
+        refA,
+      )!;
+      return resolveChatCanvasLayout({
+        container,
+        maxChatWidth: 736,
+        composerHeight: 206,
+        detailsCard: { left: 1260, right: 1572, bottom: 339 },
+        preview: { ...player, key: "browser:tab-a", source: { width: 1000, height: 1523 } },
+      });
+    };
+    const resized = layout();
+    expect(resized.frame).toEqual({ x: 1112, y: 275, width: 460, height: 701 });
+    store.move(refA, "browser:tab-a", { x: 1106, y: 275 });
+    const dragged = layout();
+    expect(dragged.frame).toEqual({ ...resized.frame, x: 1106 });
+    const card = resolveThreadDetailsCardLayout({
+      container,
+      lane: { padding: 48, minChatWidth: 640 },
+      frame: dragged.frame,
+      overlapsDetailsCard: dragged.overlapsDetailsCard,
+    })!;
+    expect(resolveThreadDetailsCardDensity(card.height, { full: 327, compact: 182 })).toBe(
+      "compact",
+    );
+  });
+
   it("ignores stale drag updates after the floating tab changes", () => {
     usePreviewMiniPlayerStore.getState().open(refA, tabA);
     usePreviewMiniPlayerStore.getState().open(refA, tabB);