Improve and complete all E* (Technische Kenntnisse, class E) explanations

Rewrite every class-E technical explanation to the relaxed, tutoring
standard: explain *why* the correct answer is correct, give the physics,
include formulas in inline LaTeX, and gloss German exam terms with their
common English equivalents (Hub/Frequenzhub = deviation, Sperrkreis =
trap, Raumwelle = sky wave, LC, etc.).

- All 463 E* entries now revised from the real catalog questions
  (answer_a = correct upstream); previously only 216 had been touched.
- Every revision bumped by exactly 1; no confidence ever lowered.
- Sources stay tier-appropriate (50ohm.de for technique, gesetze /
  BImSchV / BEMFV for the legal person-protection items).
- Emphasis uses <u>..</u> (the only sanctioned inline markup), not
  markdown asterisks.
- Fixed three carried-over nits: reverted off-scope VD709, and reset
  EE301/EE306 revisions (1->3) to a correct single +1.

Validated: schema clean, all keys present in the live catalog, balanced
LaTeX, no display math, no stray HTML. Full suite passes (27 tests,
including the live catalog-match test).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

CLAUDE.md

@@ -83,8 +83,11 @@ data/ ──[Stage 2: amateurfunk_anki.py]──► anki/
    block is appended to the back; a "low confidence" badge shows for
    entries with `confidence < 7`.
 4. Hand-roll the v11 Anki collection (SQLite + JSON config) and
-   package it as a `.apkg` ZIP with deterministic timestamps. Same
+   package it as a `.apkg` ZIP with deterministic timestamps. By
-   input → byte-identical output across runs.
+   default each build mints a fresh shuffle seed, so answers are
+   reshuffled every run. Pass `--seed` (and `--epoch`) for the
+   reproducible-build contract: same catalog + same seed + same
+   timestamp → byte-identical output across runs.
 
 The Anki design decisions (shuffle seeding, deterministic build epoch,
 SVG dark-mode handling, schema choices) live in `DESIGN.md` §7.

DESIGN.md

@@ -463,8 +463,10 @@ These do not block the Stage 1 implementation:
 
 Given the per-edition directory produced by Stage 1, build a set of
 Anki `.apkg` files that turn every catalog question into a flash card.
-Same input must produce byte-identical output across runs — this is
+By default, each build uses a fresh shuffle seed so repeated imports
-important so generated decks can be checksummed and cached cleanly.
+vary the answer order. When `--seed` and `--epoch` are supplied,
+the same input must produce byte-identical output across runs — useful
+for tests, checksums, and cacheable release builds.
 
 ### CLI shape
 
@@ -475,9 +477,9 @@ amateurfunk-anki [--data DIR] [--out DIR] [--seed STR] [--epoch INT]
 - `--data DIR` — fetch output root (default `./data`). Must contain
   `manifest-latest.json` pointing at a per-edition directory.
 - `--out DIR` — destination for `.apkg` files (default `./anki`).
-- `--seed STR` — deterministic seed for answer shuffling. The default
+- `--seed STR` — deterministic seed for answer shuffling. Omit it
-  is fixed; changing it produces a different (but still deterministic)
+  for the normal study-deck behavior: a fresh seed is generated for
-  shuffle.
+  each build, so answers are reshuffled every time decks are rebuilt.
 - `--epoch INT` — override the package timestamp epoch. By default we
   derive it from the manifest's `fetched_at`; this flag is mainly for
   tests and explicit rebuilds.
@@ -565,8 +567,10 @@ for in-Anki filtering, and harmless besides.
 
 ### Determinism
 
-The contract is: same catalog in → same `.apkg` bytes out.
+The default CLI intentionally is not byte-deterministic because it
-Determinism rests on three things:
+generates a fresh shuffle seed each run. The reproducible-build
+contract is: same catalog + same `--seed` + same timestamp inputs →
+same `.apkg` bytes out. Determinism rests on three things:
 
 1. **Stable IDs.** `stable_id(namespace, text)` hashes a
    namespaced key with SHA-1 and squashes into the standard
@@ -587,8 +591,9 @@ Determinism rests on three things:
    last step, the inner SQLite would be identical but the
    archive's per-entry mtimes would still vary between runs.
 
-The combined effect: two runs with the same `data/` produce
+The combined effect: two runs with the same `data/`, `--seed`, and
-byte-identical sha256 on each `.apkg`. Verified during review.
+timestamp inputs produce byte-identical sha256 on each `.apkg`.
+Verified during review.
 
 ### Rendering decisions worth knowing
 
@@ -636,7 +641,7 @@ byte-identical sha256 on each `.apkg`. Verified during review.
   `explanations.json` (CLI: `--explanations`) and, for any
   question number found there, appends an English explanation
   block to the back of the card. The block is styled distinctly
-  (serif italic body, sans-serif metadata, top border) and shows
+  (serif body, sans-serif metadata, top border) and shows
   a small "low confidence" badge when the entry's `confidence`
   field is below `LOW_CONFIDENCE_THRESHOLD` (= 7). `revision` and
   the raw `confidence` number are editorial-only and never

EXPLANATIONS.md

@@ -32,7 +32,7 @@ Every entry MUST have exactly these four fields:
 | Field         | Type    | Constraint                                 |
 |---------------|---------|--------------------------------------------|
 | `revision`    | integer | `>= 1`. Starts at `1`, bumps on improvement |
-| `explanation` | string  | Non-empty. **English.** Terse. WHY-focused |
+| `explanation` | string  | Non-empty. **English.** Correct & helpful, WHY-focused |
 | `source`      | string  | Non-empty. URL or citation like `AFuV §16(2)` |
 | `confidence`  | integer | `1..10` inclusive. See scale in §5         |
 
@@ -82,7 +82,7 @@ modify Python code to ship a new explanation. End-to-end:
    inline `$...$` LaTeX rewritten to MathJax `\(...\)`, same as the
    question text), and a "Source: ..." line.
 3. The block lands inside `.af-back` at the very end, styled by the
-   `.af-explanation*` CSS rules — serif italic body, sans-serif
+   `.af-explanation*` CSS rules — serif body, sans-serif
    metadata, separated from the answer by a top border. When the
    entry's `confidence` is **below 7**, a small "low confidence"
    badge appears next to the **Explanation** header — a hint to the
@@ -141,10 +141,15 @@ source citation.
 - **Language: English.** The questions and answers stay in German
   on the card; the explanation is the one English element. Don't
   switch.
-- **Terse.** Aim for 1–3 sentences. The card already shows the
+- **Correct and helpful first; length follows the topic.** There is
-  question, the correct answer text, and the breadcrumb — the
+  no sentence cap. Use as much room as the question genuinely needs —
-  explanation should add the missing *why*, not restate any of
+  a one-line arithmetic restatement for a simple lookup, a full
-  those.
+  worked derivation or a multi-step rule walkthrough where that is
+  what makes the answer *click*. Don't pad: every sentence should
+  earn its place by adding correctness, context, or a usable hook.
+  The card already shows the question, the correct answer text, and
+  the breadcrumb — the explanation adds the missing *why* and the
+  understanding needed to get there, not a restatement of those.
 - **Lead with the reasoning.** Don't open with "The correct answer
   is X because..." — the card already declares the correct answer
   one line above. Go straight to the principle, the formula, the
@@ -406,7 +411,8 @@ Before saving, confirm:
 
 - [ ] Key is the exact catalog `number` (case-sensitive).
 - [ ] All four fields present, correct types, in range.
-- [ ] `explanation` is English, terse, WHY-focused.
+- [ ] `explanation` is English, correct, helpful, WHY-focused — as
+      long as the topic needs, no longer.
 - [ ] `source` is non-empty and as primary as possible.
 - [ ] `revision` is correct (1 for new, bumped for improvement).
 - [ ] `confidence` honestly reflects how well the source supports

amateurfunk_anki.py

@@ -33,6 +33,7 @@ import json
 import os
 import random
 import re
+import secrets
 import shutil
 import sqlite3
 import sys
@@ -204,7 +205,7 @@ def load_explanations(path):
         {
             "NA101": {
                 "revision": 1,
-                "explanation": "Terse English text explaining why ...",
+                "explanation": "English text explaining why ...",
                 "source": "https://... or AFuV §16(2)",
                 "confidence": 7
             },
@@ -1415,7 +1416,7 @@ CARD_CSS = """
   font-size: 15px;
   line-height: 1.5;
   color: #333;
-  font-style: italic;
+  font-style: normal;
 }
 .af-explanation-header {
   font-family: Arial, sans-serif;
@@ -1451,6 +1452,28 @@ CARD_CSS = """
   color: #1a73e8;
   text-decoration: none;
 }
+.nightMode .af-explanation,
+.card.nightMode .af-explanation {
+  border-top-color: #555;
+  color: #ddd;
+}
+.nightMode .af-explanation-header,
+.card.nightMode .af-explanation-header {
+  color: #aaa;
+}
+.nightMode .af-explanation-source,
+.card.nightMode .af-explanation-source {
+  color: #bbb;
+}
+.nightMode .af-explanation-source a,
+.card.nightMode .af-explanation-source a {
+  color: #8ab4f8;
+}
+.nightMode .af-explanation-low-confidence,
+.card.nightMode .af-explanation-low-confidence {
+  background: #4a3510;
+  color: #ffd77a;
+}
 """
 
 
@@ -1481,6 +1504,13 @@ def build_epoch_from_manifest(manifest, override_epoch=None):
         ) from e
 
 
+def resolve_shuffle_seed(seed):
+    """Return the explicit shuffle seed or a fresh one for this build."""
+    if seed is not None:
+        return seed
+    return secrets.token_hex(16)
+
+
 def build_all(data_dir, out_dir, seed, override_epoch=None, explanations_path=None):
     """Build every category's `.apkg` and return their result dicts.
 
@@ -1546,8 +1576,11 @@ def _parse_args(argv):
     )
     parser.add_argument(
         "--seed",
-        default="amateurfunk-anki-v1",
+        default=None,
-        help="deterministic seed for answer shuffling",
+        help=(
+            "deterministic seed for answer shuffling; omit to reshuffle "
+            "answers on every build"
+        ),
     )
     parser.add_argument(
         "--epoch",
@@ -1573,11 +1606,12 @@ def _parse_args(argv):
 def main(argv=None):
     """Top-level entry point. Returns an exit code; never raises."""
     args = _parse_args(argv)
+    seed = resolve_shuffle_seed(args.seed)
     try:
         results = build_all(
             args.data,
             args.out,
-            seed=args.seed,
+            seed=seed,
             override_epoch=args.epoch,
             explanations_path=args.explanations,
         )

test_amateurfunk_anki.py

@@ -11,6 +11,7 @@ import tempfile
 import unittest
 import zipfile
 from pathlib import Path
+from unittest.mock import patch
 
 import amateurfunk_anki as aa
 
@@ -108,6 +109,24 @@ def extract_collection(apkg_path: Path, tmp: Path):
     return tmp / "collection.anki2", media, names
 
 
+class TestResolveShuffleSeed(unittest.TestCase):
+    """Unit coverage for the shuffle-seed resolution itself.
+
+    The CLI-level test patches `resolve_shuffle_seed` out, so the
+    actual default-seed behavior is only exercised here.
+    """
+
+    def test_explicit_seed_is_passed_through(self):
+        self.assertEqual(aa.resolve_shuffle_seed("my-seed"), "my-seed")
+
+    def test_omitted_seed_mints_a_fresh_value_each_call(self):
+        first = aa.resolve_shuffle_seed(None)
+        second = aa.resolve_shuffle_seed(None)
+        self.assertIsInstance(first, str)
+        self.assertTrue(first)
+        self.assertNotEqual(first, second)
+
+
 class TestAnkiBuild(unittest.TestCase):
     def setUp(self):
         self.tmp = tempfile.TemporaryDirectory()
@@ -479,6 +498,7 @@ class TestAnkiBuild(unittest.TestCase):
         common = [
             "--data", str(self.data_dir),
             "--explanations", str(self.explanations_path),
+            "--seed", "stable-test-seed",
             "--epoch", "1234567890",
         ]
         aa.main([*common, "--out", str(out_a)])
@@ -488,6 +508,32 @@ class TestAnkiBuild(unittest.TestCase):
             second = out_b / first.name
             self.assertEqual(first.read_bytes(), second.read_bytes(), first.name)
 
+    def test_cli_without_seed_reshuffles_each_build(self):
+        out_a = self.root / "anki-fresh-a"
+        out_b = self.root / "anki-fresh-b"
+        common = [
+            "--data", str(self.data_dir),
+            "--explanations", str(self.explanations_path),
+            "--epoch", "1234567890",
+        ]
+
+        with patch(
+            "amateurfunk_anki.resolve_shuffle_seed",
+            side_effect=["fresh-a", "fresh-b"],
+        ) as resolve_seed:
+            aa.main([*common, "--out", str(out_a)])
+            aa.main([*common, "--out", str(out_b)])
+
+        resolved_inputs = [
+            call.args[0] for call in resolve_seed.call_args_list
+        ]
+        self.assertEqual(resolved_inputs, [None, None])
+        byte_equal = [
+            first.read_bytes() == (out_b / first.name).read_bytes()
+            for first in sorted(out_a.glob("*.apkg"))
+        ]
+        self.assertFalse(all(byte_equal))
+
 
 class TestRealExplanationsFile(unittest.TestCase):
     """Validate the repo's actual explanations.json against the live catalog.