fix: clear alt text when the upload dialog is handed a different file

The file input's `onChange` reset `state` to `IDLE` and left `altText`
untouched. On success that is harmless -- the dialog unmounts. But
REJECTED, QUARANTINED and TRANSPORT_FAILED all leave it mounted with the
file input re-enabled, and that is precisely the retry path: upload
`db-schema.png` described as "DB 스키마", have it quarantined, pick
`sequence.png`, upload -- and `sequence.png` shipped described as
"DB 스키마", passing EVIDENCE_ALT_REQUIRED and publishing with a caption
about a different image.

Cleared on every file selection rather than only after a failure: alt
text describes one image, and "which file is this describing" has one
honest answer per selection. `submit()`'s existing ALT_REQUIRED refusal
turns the emptied field into a stop rather than a silent omission.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/features/tech-log/presentation/studio/components/asset-upload-dialog.tsx

@@ -188,8 +188,20 @@ export function AssetUploadDialog(props: Readonly<{
                 setState({ kind: "SELECTION_FAILED", message: MESSAGES.SELECTION_FAILED });
                 return;
               }
-              // A new file clears whatever the previous attempt reported.
+              // A new file clears whatever the previous attempt reported --
+              // and its description with it. Alt text describes *this image*,
+              // and every terminal failure state (REJECTED, QUARANTINED,
+              // TRANSPORT_FAILED) leaves this dialog mounted with the file
+              // input re-enabled, so the retry path is exactly where a stale
+              // description survives: upload `db-schema.png` as "DB 스키마",
+              // get it quarantined, pick `sequence.png`, upload -- and
+              // `sequence.png` ships described as "DB 스키마" and validates as
+              // publishable. Cleared unconditionally rather than only after a
+              // failure: "which file is this text describing" has one honest
+              // answer per selection, and `submit()`'s ALT_REQUIRED refusal
+              // makes the emptied field impossible to ignore.
               setState({ kind: "IDLE" });
+              setAltText("");
               if (!decorative) altRef.current?.focus();
             }}
           />

tests/features/tech-log/asset-picker.test.tsx

@@ -1835,3 +1835,76 @@ test("mergeAssetCatalog can only grow: an empty arrival keeps everything", () =>
 
   assert.deepEqual(mergeAssetCatalog([known], []).map((asset) => asset.id), [known.id]);
 });
+
+// --- Alignment follow-up, item 3: alt text must not outlive its file ---
+//
+// The file input's `onChange` reset `state` to `IDLE` and left `altText`
+// alone. On success that is harmless -- the dialog unmounts. But REJECTED,
+// QUARANTINED and TRANSPORT_FAILED all leave it mounted with the file input
+// re-enabled, which is exactly the retry path: upload `db-schema.png`
+// described as "DB 스키마", get it quarantined, pick `sequence.png`, upload --
+// and `sequence.png` shipped described as "DB 스키마", validating as
+// publishable the whole way.
+
+test("picking a different file after a quarantined upload clears the previous image's alt text", async () => {
+  const user = userEvent.setup();
+  const forms: Array<{ altText?: string; filename: string }> = [];
+  const gateway = uploadOnlyGateway(async (form) => {
+    forms.push({ altText: form.altText, filename: form.file.name });
+    return (forms.length === 1
+      ? { ...READY, managementStatus: "QUARANTINED" }
+      : READY) as never;
+  });
+  render(<AssetUploadDialog gateway={gateway} kind="IMAGE" onUploaded={() => {}} onClose={() => {}} />);
+
+  chooseAndUpload(new File(["a"], "db-schema.png", { type: "image/png" }), "DB 스키마");
+  await waitFor(() =>
+    assert.equal(
+      screen.getByRole("status", { name: "업로드 상태" }).textContent,
+      "보안 검사에서 격리되어 사용할 수 없습니다.",
+    ),
+  );
+
+  chooseFile(new File(["b"], "sequence.png", { type: "image/png" }));
+
+  assert.equal((screen.getByLabelText("대체 텍스트") as HTMLInputElement).value, "");
+  // And the emptied field is enforced, not merely displayed: uploading now
+  // refuses instead of shipping an undescribed image.
+  await user.click(screen.getByRole("button", { name: "업로드" }));
+  assert.equal(
+    screen.getByRole("status", { name: "업로드 상태" }).textContent,
+    "대체 텍스트를 입력하거나 장식용으로 표시하세요.",
+  );
+  assert.equal(forms.length, 1);
+});
+
+test("the retry after a transport failure ships its own alt text, never the first attempt's", async () => {
+  const forms: Array<{ altText?: string; filename: string }> = [];
+  const gateway = uploadOnlyGateway(async (form) => {
+    forms.push({ altText: form.altText, filename: form.file.name });
+    if (forms.length === 1) throw new Error("offline");
+    return READY as never;
+  });
+  render(<AssetUploadDialog gateway={gateway} kind="IMAGE" onUploaded={() => {}} onClose={() => {}} />);
+
+  chooseAndUpload(new File(["a"], "db-schema.png", { type: "image/png" }), "DB 스키마");
+  await waitFor(() =>
+    assert.equal(
+      screen.getByRole("status", { name: "업로드 상태" }).textContent,
+      "업로드를 전송하지 못했습니다.",
+    ),
+  );
+
+  chooseAndUpload(new File(["b"], "sequence.png", { type: "image/png" }), "시퀀스 다이어그램");
+  await waitFor(() =>
+    assert.equal(
+      screen.getByRole("status", { name: "업로드 상태" }).textContent,
+      "업로드했습니다.",
+    ),
+  );
+
+  assert.deepEqual(forms, [
+    { altText: "DB 스키마", filename: "db-schema.png" },
+    { altText: "시퀀스 다이어그램", filename: "sequence.png" },
+  ]);
+});