feat(gui): tool pages pick up the home-page upload via session_state

Closes the last UX gap from the analyzer review: each tool page had its
own st.file_uploader, so users had to upload the same file twice (once
on the home page for analysis, once on each tool page).

components.pickup_or_upload(label, key, types) returns either:
  - a _StashedUpload shim wrapping the home-page bytes (when present and
    the user hasn't asked for a different file on this page), or
  - the standard st.file_uploader (when nothing is stashed or the user
    clicked "Use a different file").

_StashedUpload duck-types Streamlit's UploadedFile (.name, .size,
.getvalue(), .read()) so existing tool-page code consumes it without
changes. A "Use a different file" button per page sets a session-state
override flag; a "Switch back to upload-screen file" button clears it.

Wired into 2_Text_Cleaner.py and 1_Deduplicator.py — the two pages with
working uploaders today. The remaining stub pages adopt it when they're
implemented; the helper is the public surface they'll use.

Verified by smoke-launching streamlit headless and curling the home,
text-cleaner, and deduplicator routes — all return 200 with no errors
in the server log.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/gui/components.py

@@ -903,3 +903,76 @@ def findings_count_for_tool(tool_id: str) -> int:
     """
     findings = st.session_state.get("home_findings") or []
     return sum(1 for f in findings if f.tool == tool_id)
+
+
+# ---------------------------------------------------------------------------
+# Cross-page upload pickup
+# ---------------------------------------------------------------------------
+
+class _StashedUpload:
+    """Duck-types ``st.runtime.uploaded_file_manager.UploadedFile`` enough
+    for the tool pages: ``.name``, ``.size``, ``.getvalue()``.
+
+    Tool pages that previously consumed a Streamlit ``UploadedFile`` can
+    accept this in its place without changes.
+    """
+
+    __slots__ = ("name", "size", "_data")
+
+    def __init__(self, name: str, data: bytes) -> None:
+        self.name = name
+        self.size = len(data)
+        self._data = data
+
+    def getvalue(self) -> bytes:
+        return self._data
+
+    def read(self) -> bytes:
+        return self._data
+
+
+def pickup_or_upload(
+    *,
+    label: str,
+    key: str,
+    types: list[str],
+    help: str | None = None,
+):
+    """Return an upload object, preferring the home-page upload when present.
+
+    Behavior:
+
+    - If ``st.session_state['home_uploaded_bytes']`` is set and the user
+      hasn't asked for a different file on this page, render a banner
+      ("Using *<name>* from upload screen") plus a "Use a different file"
+      button, and return a :class:`_StashedUpload` shim.
+    - Otherwise render the standard ``st.file_uploader`` with the supplied
+      *label*, *key*, and *types*. Returns the Streamlit ``UploadedFile``
+      directly (or ``None`` if nothing uploaded).
+
+    The ``_StashedUpload`` shim exposes ``.name``, ``.size``, and
+    ``.getvalue()`` so existing tool-page code that consumes a Streamlit
+    upload object works without changes.
+    """
+    override_key = f"{key}__override"
+    has_session_upload = st.session_state.get("home_uploaded_bytes") is not None
+    use_session = has_session_upload and not st.session_state.get(override_key, False)
+
+    if use_session:
+        name = st.session_state.get("home_uploaded_name", "uploaded file")
+        st.info(f"Using **{name}** from the upload screen.")
+        if st.button("Use a different file", key=f"{key}__pick_diff"):
+            st.session_state[override_key] = True
+            st.rerun()
+        return _StashedUpload(name, st.session_state["home_uploaded_bytes"])
+
+    uploaded = st.file_uploader(label, type=types, key=key, help=help)
+    if uploaded is not None and st.session_state.get(override_key):
+        # User has uploaded their own file on this page; clear the override
+        # so the next visit to a tool page starts fresh.
+        pass
+    if uploaded is None and st.session_state.get(override_key) and has_session_upload:
+        if st.button("Switch back to upload-screen file", key=f"{key}__switch_back"):
+            st.session_state[override_key] = False
+            st.rerun()
+    return uploaded

src/gui/pages/1_Deduplicator.py

@@ -21,6 +21,7 @@ from src.gui.components import (
     config_panel,
     hide_streamlit_chrome,
     match_group_card,
+    pickup_or_upload,
     results_summary,
 )
 
@@ -56,11 +57,11 @@ st.caption("Find and remove duplicate rows in CSV, delimited text, and Excel fil
 # File upload
 # ---------------------------------------------------------------------------
 
-uploaded = st.file_uploader(
-    "Upload CSV or Excel file",
-    type=["csv", "tsv", "xlsx", "xls"],
-    help="Supports CSV, TSV, and Excel files. Encoding and delimiters are auto-detected.",
+uploaded = pickup_or_upload(
+    label="Upload CSV or Excel file",
     key="dedup_file_upload",
+    types=["csv", "tsv", "xlsx", "xls"],
+    help="Supports CSV, TSV, and Excel files. Encoding and delimiters are auto-detected.",
 )
 
 if uploaded is not None:

src/gui/pages/2_Text_Cleaner.py

@@ -14,7 +14,7 @@ _project_root = Path(__file__).resolve().parent.parent.parent.parent
 if str(_project_root) not in sys.path:
     sys.path.insert(0, str(_project_root))
 
-from src.gui.components import hide_streamlit_chrome
+from src.gui.components import hide_streamlit_chrome, pickup_or_upload
 from src.core.text_clean import (
     PRESETS,
     CleanOptions,
@@ -38,10 +38,10 @@ st.caption(
 # File upload
 # ---------------------------------------------------------------------------
 
-uploaded = st.file_uploader(
-    "Upload CSV or Excel file",
-    type=["csv", "tsv", "xlsx", "xls"],
+uploaded = pickup_or_upload(
+    label="Upload CSV or Excel file",
     key="textclean_file_upload",
+    types=["csv", "tsv", "xlsx", "xls"],
 )
 
 if uploaded is None: