feat: replace the completions store with per-event progress

Membership in a set can only say "done", so "started" was inexpressible.
Progress carries a status instead, plus an optional effort estimate and a
note.

The old completions key is read once to seed status: "done", and is never
written to or deleted. Someone who last opened the app six months ago still
has their marks under it, these live only in the browser, and nothing else
holds a copy to restore from.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

src/client/state/storage.ts

@@ -11,7 +11,13 @@
 const NS = "gacha-tracker:v1";
 
 export const KEYS = {
+  /**
+   * Superseded by `progress`, which carries a status rather than using
+   * membership to mean "done". Read once to migrate; never written, never
+   * deleted — see useProgress.
+   */
   completions: `${NS}:completions`,
+  progress: `${NS}:progress`,
   ignored: `${NS}:ignored`,
   prefs: `${NS}:prefs`,
 } as const;

src/client/state/useProgress.ts

@@ -0,0 +1,129 @@
+import { useCallback, useEffect, useState } from "react";
+import type { Effort } from "../../shared/effort.ts";
+import { KEYS, readJson, writeJson } from "./storage.ts";
+import type { Marks } from "./useMarkSet.ts";
+
+/** Where the reader is with an event. Absent means untouched. */
+export type Status = "doing" | "done";
+
+export interface Progress {
+  status?: Status | undefined;
+  effort?: Effort | undefined;
+  /** Anything the reader wants to remember about it. */
+  note?: string | undefined;
+  at: string;
+}
+
+export type ProgressMap = Record<string, Progress>;
+
+/**
+ * Per-event notes the reader adds: where they are with it, how much work they
+ * think it is, and anything else worth remembering.
+ *
+ * Supersedes the completions-only store. Completions were `{ [id]: { at } }`
+ * with membership meaning "done"; this carries a status instead, so "started"
+ * is expressible.
+ *
+ * MIGRATION: the old completions store is read once to seed `status: "done"`,
+ * and is **never written to or deleted**. Someone who last opened the app six
+ * months ago still has their marks under that key, and these live only in the
+ * browser — nothing else holds a copy to restore from. See
+ * docs/DATA-MODEL.md § Client-side storage.
+ */
+function load(): ProgressMap {
+  const stored = readJson<ProgressMap>(KEYS.progress, {});
+  if (Object.keys(stored).length > 0) return stored;
+
+  const legacy = readJson<Marks>(KEYS.completions, {});
+  const seeded: ProgressMap = {};
+  for (const [id, mark] of Object.entries(legacy)) {
+    seeded[id] = { status: "done", at: mark.at };
+  }
+  return seeded;
+}
+
+export function useProgress() {
+  const [progress, setProgress] = useState<ProgressMap>(load);
+
+  useEffect(() => {
+    writeJson(KEYS.progress, progress);
+  }, [progress]);
+
+  const patch = useCallback((id: string, next: Partial<Progress>) => {
+    setProgress((prev) => {
+      const merged: Progress = {
+        ...prev[id],
+        ...next,
+        at: new Date().toISOString(),
+      };
+      // An entry with nothing recorded is not worth keeping; drop it so the
+      // store stays a set of things the reader actually said something about.
+      if (
+        merged.status === undefined &&
+        merged.effort === undefined &&
+        (merged.note ?? "") === ""
+      ) {
+        const { [id]: _removed, ...rest } = prev;
+        return rest;
+      }
+      return { ...prev, [id]: merged };
+    });
+  }, []);
+
+  const setStatus = useCallback(
+    (id: string, status: Status | undefined) => patch(id, { status }),
+    [patch],
+  );
+
+  const cycleStatus = useCallback(
+    (id: string) => {
+      setProgress((prev) => {
+        // Untouched → doing → done → untouched. One control, three states, in
+        // the order the reader actually moves through them.
+        const current = prev[id]?.status;
+        const next: Status | undefined =
+          current === undefined ? "doing" : current === "doing" ? "done" : undefined;
+        const merged: Progress = {
+          ...prev[id],
+          status: next,
+          at: new Date().toISOString(),
+        };
+        if (
+          merged.status === undefined &&
+          merged.effort === undefined &&
+          (merged.note ?? "") === ""
+        ) {
+          const { [id]: _removed, ...rest } = prev;
+          return rest;
+        }
+        return { ...prev, [id]: merged };
+      });
+    },
+    [],
+  );
+
+  const setEffort = useCallback(
+    (id: string, effort: Effort | undefined) => patch(id, { effort }),
+    [patch],
+  );
+
+  const setNote = useCallback(
+    (id: string, note: string) => patch(id, { note: note.trim() }),
+    [patch],
+  );
+
+  /** Union merge on import, keeping the earlier entry. Never removes. */
+  const merge = useCallback((incoming: ProgressMap) => {
+    setProgress((prev) => {
+      const next = { ...prev };
+      for (const [id, value] of Object.entries(incoming)) {
+        const existing = next[id];
+        next[id] =
+          existing === undefined || value.at < existing.at ? value : existing;
+      }
+      return next;
+    });
+  }, []);
+
+  return { progress, patch, setStatus, cycleStatus, setEffort, setNote, merge };
+}