Add per-row session delete + Reset all data; fix viewer URL fallback

UX gaps that surfaced while running the demo:

- ViewerShell hardcoded `/fixtures/pdfs/<title>` for the PDF URL,
  ignoring the `document.uri` blob URL that uploaded PDFs carry. The
  viewer either 404'd or — worse — silently served a fixture whose
  filename happened to collide. Prefer document.uri when present.

- SessionMenu only let you delete the *active* session. Added a small
  per-row "✕" button next to every session in the Switch-to list so a
  user can drop a session's data without first switching to it. Same
  click-to-confirm pattern as the existing Delete action.

- Added a "Reset all data…" affordance in both the SessionMenu and the
  empty-state landing. Calls a new `clearAllSessionData()` helper that
  wipes every `citation-evidence:*` key from localStorage, then forces
  a reload so all in-memory caches start fresh.

- `attachSessionPersister.writeOnDelete` was leaking the per-session
  `active-document-id:v1` key on every session delete. Now removed
  alongside the engine snapshot key.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/sessions/SessionMenu.tsx

@@ -13,8 +13,10 @@
 import { useCallback, useEffect, useMemo, useRef, useState } from "react";
 import type { CSSProperties } from "react";
 
+import type { SessionId } from "@shared/ids";
 import type { Session } from "@shared/session";
 import { useActiveSession, useSessionListTick, useSessionService } from "@work/index";
+import { clearAllSessionData } from "@engine/index";
 
 import { navigateTo } from "./routing";
 
@@ -35,6 +37,9 @@ export function SessionMenu({ onExportZip, onImportZip, onOpenSamples }: Session
   const [renaming, setRenaming] = useState(false);
   const [renameValue, setRenameValue] = useState("");
   const [pendingDelete, setPendingDelete] = useState(false);
+  /** Per-row delete confirmation: id of the session armed for delete. */
+  const [pendingRowDelete, setPendingRowDelete] = useState<SessionId | null>(null);
+  const [pendingResetAll, setPendingResetAll] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const wrapperRef = useRef<HTMLDivElement | null>(null);
 
@@ -60,12 +65,28 @@ export function SessionMenu({ onExportZip, onImportZip, onOpenSamples }: Session
         setCreating(false);
         setRenaming(false);
         setPendingDelete(false);
+        setPendingRowDelete(null);
+        setPendingResetAll(false);
       }
     };
     window.addEventListener("mousedown", handler);
     return () => window.removeEventListener("mousedown", handler);
   }, [open]);
 
+  // Auto-clear pending row-delete after a few seconds so the user
+  // doesn't accidentally double-click much later and lose data.
+  useEffect(() => {
+    if (!pendingRowDelete) return;
+    const t = setTimeout(() => setPendingRowDelete(null), 3000);
+    return () => clearTimeout(t);
+  }, [pendingRowDelete]);
+
+  useEffect(() => {
+    if (!pendingResetAll) return;
+    const t = setTimeout(() => setPendingResetAll(false), 5000);
+    return () => clearTimeout(t);
+  }, [pendingResetAll]);
+
   const switchTo = useCallback(
     (sessionId: import("@shared/ids").SessionId) => {
       navigateTo({ sessionId, mode: "review" });
@@ -111,6 +132,41 @@ export function SessionMenu({ onExportZip, onImportZip, onOpenSamples }: Session
     navigateTo({ sessionId: null, mode: "review" });
   }, [active, pendingDelete, service]);
 
+  const handleRowDelete = useCallback(
+    (e: React.MouseEvent, id: SessionId) => {
+      e.stopPropagation();
+      if (pendingRowDelete !== id) {
+        setPendingRowDelete(id);
+        return;
+      }
+      const wasActive = active?.id === id;
+      service.delete(id);
+      setPendingRowDelete(null);
+      if (wasActive) {
+        setOpen(false);
+        navigateTo({ sessionId: null, mode: "review" });
+      }
+    },
+    [active, pendingRowDelete, service],
+  );
+
+  const handleResetAll = useCallback(() => {
+    if (!pendingResetAll) {
+      setPendingResetAll(true);
+      return;
+    }
+    clearAllSessionData();
+    setPendingResetAll(false);
+    setOpen(false);
+    // Force a full reload so every in-memory cache (sessions repo,
+    // byte stores, engine snapshots) starts fresh from the cleared
+    // localStorage.
+    if (typeof window !== "undefined") {
+      window.location.hash = "";
+      window.location.reload();
+    }
+  }, [pendingResetAll]);
+
   return (
     <div ref={wrapperRef} style={{ position: "relative" }} data-testid="session-menu">
       <button
@@ -155,22 +211,48 @@ export function SessionMenu({ onExportZip, onImportZip, onOpenSamples }: Session
               <div style={{ padding: "4px 8px", color: "#666", fontSize: 11 }}>
                 Switch to…
               </div>
-              {sessions.map((s) => (
-                <button
-                  key={s.id}
-                  type="button"
-                  role="menuitem"
-                  data-testid={`session-switch-${s.id}`}
-                  onClick={() => switchTo(s.id)}
-                  style={{
-                    ...menuItemStyle,
-                    background: active?.id === s.id ? "#e8f0ff" : "transparent",
-                  }}
-                >
-                  {s.name}
-                  {active?.id === s.id ? " · open" : ""}
-                </button>
-              ))}
+              {sessions.map((s) => {
+                const rowArmed = pendingRowDelete === s.id;
+                return (
+                  <div
+                    key={s.id}
+                    style={{
+                      display: "flex",
+                      alignItems: "center",
+                      background: active?.id === s.id ? "#e8f0ff" : "transparent",
+                    }}
+                  >
+                    <button
+                      type="button"
+                      role="menuitem"
+                      data-testid={`session-switch-${s.id}`}
+                      onClick={() => switchTo(s.id)}
+                      style={{ ...menuItemStyle, flex: 1 }}
+                    >
+                      {s.name}
+                      {active?.id === s.id ? " · open" : ""}
+                    </button>
+                    <button
+                      type="button"
+                      aria-label={`Delete session ${s.name}`}
+                      data-testid={`session-row-delete-${s.id}`}
+                      onClick={(e) => handleRowDelete(e, s.id)}
+                      title={rowArmed ? "Click again to confirm" : "Delete session and drop all its data"}
+                      style={{
+                        background: rowArmed ? "#ffe5e5" : "transparent",
+                        border: "none",
+                        color: "#7a0000",
+                        cursor: "pointer",
+                        padding: "4px 8px",
+                        fontSize: 14,
+                        lineHeight: 1,
+                      }}
+                    >
+                      {rowArmed ? "Confirm?" : "✕"}
+                    </button>
+                  </div>
+                );
+              })}
               <hr style={dividerStyle} />
             </>
           )}
@@ -316,6 +398,20 @@ export function SessionMenu({ onExportZip, onImportZip, onOpenSamples }: Session
             </button>
           )}
 
+          <hr style={dividerStyle} />
+          <button
+            type="button"
+            role="menuitem"
+            data-testid="session-menu-reset-all"
+            onClick={handleResetAll}
+            title="Wipe every session, every uploaded PDF, every annotation — and reload."
+            style={{ ...menuItemStyle, color: "#7a0000" }}
+          >
+            {pendingResetAll
+              ? "Confirm — wipe everything?"
+              : "Reset all data…"}
+          </button>
+
           {error && (
             <div
               data-testid="session-menu-error"