audit: no dead end survives a corrupt record, no lie survives a filesystem error

- a blank summary record bricked wake forever: it refused with 'Do the 0
  compressions below' + a literal None, while nap said nothing was left.
  Both sites (wake's cover, nap's half) now name the one exit: forget.
- tree_get/count/repair swallowed every OSError as 'not built yet', so an
  unreadable level was reported as pending work that could not be done.
  Only FileNotFoundError means absent; real failures surface with the path.
- import accepted 2026-99-99, poisoning the store's date order forever.
- the wake T error now says 'the log holds N memories', not 'entries'.

memo

@@ -205,7 +205,7 @@ def tree_path(d, size):
 def count(path, rec):
     try:
         return os.path.getsize(path) // rec
-    except OSError:
+    except FileNotFoundError:  # any other failure is real and must surface
         return 0
 
 
@@ -219,7 +219,7 @@ def repair(path, rec):
     every later record is misaligned. Callers hold the lock."""
     try:
         n = os.path.getsize(path)
-    except OSError:
+    except FileNotFoundError:
         return
     if n % rec:
         with open(path, "r+b") as f:
@@ -271,7 +271,7 @@ def tree_get(d, lo, hi):
         with open(tree_path(d, size), "rb") as f:
             f.seek((lo // size) * TREE_REC)
             rec = f.read(TREE_REC)
-    except OSError:
+    except FileNotFoundError:  # not built yet; any other failure is real
         return None
     return rec.decode().rstrip() or None
 
@@ -425,7 +425,11 @@ def nap_prompt(d, lo, hi, left):
         for a, b in ((lo, mid), (mid, hi)):
             s = tree_get(d, a, b)
             if s is None:
-                die("Summary %d-%d is missing. Run: %s nap" % (a, b - 1, ME))
+                # pending() lists a block only after its halves settled, so
+                # a missing half is a blank record -- a corrupt write. Drop
+                # it and the next nap rebuilds it.
+                die("The summary of #%d-%d is blank. Run: %s forget %d-%d"
+                    % (a, b - 1, ME, a, b - 1))
             halves.append("  #%d-%d %s" % (a, b - 1, s))
         body = "\n".join(halves)
     tail = "" if not left else "\n%s after this one." % (
@@ -537,8 +541,8 @@ def cmd_wake(d, args):
         if len(args) == 2:
             T = int(args[1])
             if T > now:
-                die("T=%d, but the memory holds %s. Run: %s wake"
-                    % (T, plural(now, "entry"), ME))
+                die("T=%d, but the log holds %s. Run: %s wake"
+                    % (T, plural(now, "memory"), ME))
     # A part is rendered as of T, so a note landing between two parts cannot
     # shift a boundary and drop a line.
     if not T:
@@ -553,17 +557,25 @@ def cmd_wake(d, args):
         else:
             s = tree_get(d, lo, hi)
             if s is None:
-                # The ONLY reason to refuse: this document cannot be written
-                # without that summary. Work that the document does not need
-                # is handed over after the read instead, costing no round
-                # trip.
-                print("Cannot wake: the memory context needs #%d-%d, which is "
-                      "not compressed yet.\nDo the %s below, then run %s "
-                      "wake again.\n"
-                      % (lo, hi - 1,
-                         plural(pending_count(d, T), "compression"), ME))
-                print(next_nap(d, T))
-                sys.exit(1)
+                nap = next_nap(d, T)
+                if nap:
+                    # The ONLY reason to refuse: this document cannot be
+                    # written without that summary. Work that the document
+                    # does not need is handed over after the read instead,
+                    # costing no round trip.
+                    print("Cannot wake: the memory context needs #%d-%d, "
+                          "which is not compressed yet.\nDo the %s below, "
+                          "then run %s wake again.\n"
+                          % (lo, hi - 1,
+                             plural(pending_count(d, T), "compression"), ME))
+                    print(nap)
+                    sys.exit(1)
+                s = tree_get(d, lo, hi)  # a parallel session may have paid it
+            if s is None:
+                # Nothing is pending, so the record exists but is blank -- a
+                # corrupt write. Drop it and the next nap rebuilds it.
+                die("The summary of #%d-%d is blank. Run: %s forget %d-%d"
+                    % (lo, hi - 1, ME, lo, hi - 1))
             lines.append("#%d-%d %s" % (lo, hi - 1, s))
     parts = paginate(lines)
     if not 1 <= k <= len(parts):
@@ -712,6 +724,10 @@ def cmd_import(d, args):
         date, _, text = line.partition(" ")
         if not re.fullmatch(r"\d{4}-\d{2}-\d{2}", date):
             die("line %d: expected 'YYYY-MM-DD <text>', got: %s" % (i, line))
+        try:
+            datetime.datetime.strptime(date, "%Y-%m-%d")
+        except ValueError:
+            die("line %d: %s is not a real date." % (i, date))
         if date < last:
             die("line %d: date %s precedes the previous memory (%s)."
                 % (i, date, last))

test.py

@@ -431,6 +431,57 @@ r = run("wake", store=d2)
 check(r.stdout.rstrip().endswith("You are awake."),
       "a one-part wake never says `You are awake.`:\n" + r.stdout)
 
+# a blank summary record (a corrupt write) is work nap cannot see: wake must
+# name the one exit, `forget`, instead of refusing forever
+d3 = tempfile.mkdtemp(prefix="optmem-blank-")
+for i in range(4):
+    run("note", "corrupt store memory %d" % i, store=d3)
+for bid, s in (("0-1", "one"), ("2-3", "two"), ("0-3", "all")):
+    run("nap", bid, s, store=d3)
+with open(os.path.join(d3, "config"), "w") as f:
+    f.write("WAKE_LINES = 2\n")
+with open(os.path.join(d3, "TREE", "2"), "r+b") as f:
+    f.write(b" " * 287 + b"\n")
+r = run("wake", store=d3)
+check(r.returncode == 1 and "forget 0-1" in r.stderr
+      and "None" not in r.stdout,
+      "a blank summary must point at forget:\n" + r.stdout + r.stderr)
+
+# an unreadable level is a filesystem failure and must surface as one --
+# reading it as "not compressed yet" offers work that cannot be done
+os.chmod(os.path.join(d3, "TREE", "2"), 0)
+r_ = subprocess.run(memo + ["wake"], capture_output=True, text=True,
+                    env=dict(os.environ, MEMORY_DIR=d3))
+check(r_.returncode == 1 and "Permission denied" in r_.stderr
+      and "not compressed" not in r_.stdout,
+      "an unreadable level was read as pending work: " + r_.stdout + r_.stderr)
+os.chmod(os.path.join(d3, "TREE", "2"), 0o644)
+
+# an impossible calendar date would poison every later import: the store's
+# order check compares against it forever
+with open(os.path.join(d3, "bad.txt"), "w") as f:
+    f.write("2027-99-99 an impossible date\n")
+r = run("import", os.path.join(d3, "bad.txt"), store=d3)
+check(r.returncode == 1 and "not a real date" in r.stderr,
+      "import accepted an impossible date: " + r.stdout + r.stderr)
+shutil.rmtree(d3)
+
+# the same blank-record dead end at the other site: a big block's half
+d4 = tempfile.mkdtemp(prefix="optmem-half-")
+for i in range(32):
+    run("note", "half probe memory %d" % i, store=d4)
+while True:
+    r = run("nap", store=d4)
+    if "Compress memories #0-31 " in r.stdout:
+        break
+    run("nap", nap_id(r.stdout), "settled", store=d4)
+with open(os.path.join(d4, "TREE", "16"), "r+b") as f:
+    f.write(b" " * 287 + b"\n")
+r = run("nap", store=d4)
+check(r.returncode == 1 and "forget 0-15" in r.stderr,
+      "a blank half summary must point at forget: " + r.stdout + r.stderr)
+shutil.rmtree(d4)
+
 # re-running init on a lived-in store must not touch one byte of it: the
 # whole setup is idempotent, so it is safe on every provision. `init` only
 # ever makedirs(exist_ok), opens LOG.txt for APPEND, and writes `config`