diff --git a/00-META/checks/README.md b/00-META/checks/README.md
index db781d6..4a1e7c2 100644
--- a/00-META/checks/README.md
+++ b/00-META/checks/README.md
@@ -1,7 +1,9 @@
 # Checks
 
 ```
-python3 00-META/checks/records.py
+python3 00-META/checks/records.py      structure: links, citations, supersession, topics
+python3 00-META/checks/index.py        the reading order in 02-DECISIONS/README.md is current
+python3 00-META/checks/index.py --write  regenerate it
 ```
 
 Non-zero exit on any problem, so it can be a gate rather than a report.
@@ -22,6 +24,8 @@ indistinguishable from one that cannot.
 | `live-citation` | a governing document citing a **superseded** record names its replacement in the same paragraph | `01-to-be/README.md` citing ADR 0022 as live guidance |
 | `supersession` | if A says it was superseded by B, B says it supersedes A | ADR 0012 never declared that it superseded 0011 |
 | `numbering` | the number in the filename is the number in the heading | — |
+| `topics` | every record names a topic the index knows | — |
+| *(index.py)* | the written reading order matches what the records say | — |
 
 ## What is deliberately not checked
 
diff --git a/00-META/checks/index.py b/00-META/checks/index.py
new file mode 100644
index 0000000..22a2f80
--- /dev/null
+++ b/00-META/checks/index.py
@@ -0,0 +1,108 @@
+#!/usr/bin/env python3
+"""Generate the decision index, and check the written one still matches.
+
+A number identifies a record and never changes, so the folder listing is creation order rather
+than reading order. The index is what carries the path — and it is written rather than only
+generated on demand, because a reader on a forge sees the folder and not a command.
+
+The objection to a written index is that it drifts. That objection is answered by checking it
+rather than by refusing to write one, which is `how-we-build` §5: a rule states how it is
+checked.
+
+    python3 00-META/checks/index.py --write     regenerate it
+    python3 00-META/checks/index.py             fail if it is stale
+"""
+
+import glob
+import io
+import os
+import re
+import sys
+
+README = "02-DECISIONS/README.md"
+START = "<!-- index:start -->"
+END = "<!-- index:end -->"
+
+# The reading order. Topics a record may belong to, in the order somebody would learn the system.
+TOPICS = [
+    ("the mesh", "What the mesh is"),
+    ("the tiers", "Its tiers, from the bottom up"),
+    ("what runs on it", "What runs on them, and how it gets there"),
+    ("building it", "How it is built"),
+    ("checking it", "How it is checked"),
+    ("how we work", "How we work"),
+]
+
+
+def field(text, name):
+    m = re.search(r'^%s:\s*(.+)$' % name, text, re.M)
+    return m.group(1).strip() if m else None
+
+
+def records():
+    out = []
+    for path in sorted(glob.glob('02-DECISIONS/0*.md')):
+        text = io.open(path, encoding='utf-8').read()
+        heading = re.search(r'^# \d+\.\s*(.+)$', text, re.M)
+        out.append({
+            "file": os.path.basename(path),
+            "number": os.path.basename(path)[:4],
+            "title": heading.group(1).strip() if heading else "(no heading)",
+            "topic": field(text, "topic"),
+            "status": field(text, "status"),
+        })
+    return out
+
+
+def render(rs):
+    known = {t for t, _ in TOPICS}
+    lines = [START, ""]
+    for topic, label in TOPICS:
+        rows = [r for r in rs if r["topic"] == topic]
+        if not rows:
+            continue
+        lines.append("### %s" % label)
+        lines.append("")
+        for r in rows:
+            mark = "" if r["status"] == "accepted" else "  *(%s)*" % r["status"]
+            lines.append("- **%s** — [%s](%s)%s" % (r["number"], r["title"], r["file"], mark))
+        lines.append("")
+    stray = [r for r in rs if r["topic"] not in known]
+    if stray:
+        lines.append("### Unfiled")
+        lines.append("")
+        for r in stray:
+            lines.append("- **%s** — [%s](%s) — `topic:` is %r, which is not one of %s" % (
+                r["number"], r["title"], r["file"], r["topic"], ", ".join(sorted(known))))
+        lines.append("")
+    lines.append(END)
+    return "\n".join(lines)
+
+
+def main():
+    text = io.open(README, encoding='utf-8').read()
+    wanted = render(records())
+
+    if START not in text or END not in text:
+        print("index: %s has no index markers (%s / %s)" % (README, START, END))
+        return 1
+
+    current = text[text.index(START):text.index(END) + len(END)]
+    if "--write" in sys.argv:
+        if current == wanted:
+            print("index: already current")
+            return 0
+        io.open(README, 'w', encoding='utf-8').write(text.replace(current, wanted, 1))
+        print("index: written")
+        return 0
+
+    if current != wanted:
+        print("index: %s is stale. Regenerate it:\n"
+              "    python3 00-META/checks/index.py --write" % README)
+        return 1
+    print("index: current")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/00-META/checks/records.py b/00-META/checks/records.py
index 4730d40..e36f96e 100644
--- a/00-META/checks/records.py
+++ b/00-META/checks/records.py
@@ -251,6 +251,25 @@ def check_supersession_symmetry(failures, records):
             )
 
 
+def check_topics(failures, records):
+    """Every record names a topic the index knows.
+
+    The topic is what puts a record in the reading order, so a record without one — or with one
+    nobody defined — disappears from the index rather than appearing in the wrong place. That is
+    the quiet failure, so it is the one checked.
+    """
+    known = {"the mesh", "the tiers", "what runs on it", "building it", "checking it",
+             "how we work"}
+    for number, record in sorted(records.items()):
+        topic = record["front"].get("topic")
+        if not topic:
+            failures.add("topics", rel(record["path"]),
+                         "no topic, so it has no place in the reading order")
+        elif topic not in known:
+            failures.add("topics", rel(record["path"]),
+                         "topic %r is not one of: %s" % (topic, ", ".join(sorted(known))))
+
+
 def check_numbering(failures, records):
     """The number in the filename is the number in the heading."""
     for number, record in records.items():
@@ -273,6 +292,7 @@ def main():
     check_live_citations(failures, records)
     check_supersession_symmetry(failures, records)
     check_numbering(failures, records)
+    check_topics(failures, records)
     print(f"records: {len(records)} decision records checked")
     return failures.report()
 
diff --git a/02-DECISIONS/0001-mesh-brokers-nodes-host-agents-think.md b/02-DECISIONS/0001-mesh-brokers-nodes-host-agents-think.md
index 6b82f90..0e437fa 100644
--- a/02-DECISIONS/0001-mesh-brokers-nodes-host-agents-think.md
+++ b/02-DECISIONS/0001-mesh-brokers-nodes-host-agents-think.md
@@ -1,4 +1,5 @@
 ---
+topic: the mesh
 status: accepted
 date: 2026-08-22
 deciders: jochen
diff --git a/02-DECISIONS/0002-nodes-communicate-over-a-broker.md b/02-DECISIONS/0002-nodes-communicate-over-a-broker.md
index 564a1ff..b548c9b 100644
--- a/02-DECISIONS/0002-nodes-communicate-over-a-broker.md
+++ b/02-DECISIONS/0002-nodes-communicate-over-a-broker.md
@@ -1,4 +1,5 @@
 ---
+topic: the mesh
 status: accepted
 date: 2026-02-25
 deciders: jochen
diff --git a/02-DECISIONS/0003-agents-are-persistent-employees.md b/02-DECISIONS/0003-agents-are-persistent-employees.md
index f6683a5..5bbe516 100644
--- a/02-DECISIONS/0003-agents-are-persistent-employees.md
+++ b/02-DECISIONS/0003-agents-are-persistent-employees.md
@@ -1,4 +1,5 @@
 ---
+topic: the mesh
 status: accepted
 date: 2026-07-12
 deciders: jochen
diff --git a/02-DECISIONS/0004-a-node-and-how-it-joins.md b/02-DECISIONS/0004-a-node-and-how-it-joins.md
index 094a971..1725bbc 100644
--- a/02-DECISIONS/0004-a-node-and-how-it-joins.md
+++ b/02-DECISIONS/0004-a-node-and-how-it-joins.md
@@ -1,4 +1,5 @@
 ---
+topic: the tiers
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0005-the-node-host.md b/02-DECISIONS/0005-the-node-host.md
index ac7875e..7afc763 100644
--- a/02-DECISIONS/0005-the-node-host.md
+++ b/02-DECISIONS/0005-the-node-host.md
@@ -1,4 +1,5 @@
 ---
+topic: the tiers
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0006-the-substrate-and-the-control-plane.md b/02-DECISIONS/0006-the-substrate-and-the-control-plane.md
index 875c67b..2401471 100644
--- a/02-DECISIONS/0006-the-substrate-and-the-control-plane.md
+++ b/02-DECISIONS/0006-the-substrate-and-the-control-plane.md
@@ -1,4 +1,5 @@
 ---
+topic: the tiers
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0007-connectivity.md b/02-DECISIONS/0007-connectivity.md
index d4cd531..086d889 100644
--- a/02-DECISIONS/0007-connectivity.md
+++ b/02-DECISIONS/0007-connectivity.md
@@ -1,4 +1,5 @@
 ---
+topic: the tiers
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0008-a-context-owns-its-store.md b/02-DECISIONS/0008-a-context-owns-its-store.md
index 155962d..b3d1015 100644
--- a/02-DECISIONS/0008-a-context-owns-its-store.md
+++ b/02-DECISIONS/0008-a-context-owns-its-store.md
@@ -1,4 +1,5 @@
 ---
+topic: the tiers
 status: accepted
 date: 2026-08-26
 deciders: jochen
diff --git a/02-DECISIONS/0009-modules-and-the-graph.md b/02-DECISIONS/0009-modules-and-the-graph.md
index e9db517..d127ba9 100644
--- a/02-DECISIONS/0009-modules-and-the-graph.md
+++ b/02-DECISIONS/0009-modules-and-the-graph.md
@@ -1,4 +1,5 @@
 ---
+topic: what runs on it
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0010-delivery.md b/02-DECISIONS/0010-delivery.md
index 716586a..74f1b73 100644
--- a/02-DECISIONS/0010-delivery.md
+++ b/02-DECISIONS/0010-delivery.md
@@ -1,4 +1,5 @@
 ---
+topic: what runs on it
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0011-managed-files-are-generated-never-edited.md b/02-DECISIONS/0011-managed-files-are-generated-never-edited.md
index f7752ef..6bcb1cd 100644
--- a/02-DECISIONS/0011-managed-files-are-generated-never-edited.md
+++ b/02-DECISIONS/0011-managed-files-are-generated-never-edited.md
@@ -1,4 +1,5 @@
 ---
+topic: building it
 status: accepted
 date: 2026-04-03
 deciders: jochen
diff --git a/02-DECISIONS/0012-the-mesh-creates-no-symlinks.md b/02-DECISIONS/0012-the-mesh-creates-no-symlinks.md
index 40fe34e..6d513a6 100644
--- a/02-DECISIONS/0012-the-mesh-creates-no-symlinks.md
+++ b/02-DECISIONS/0012-the-mesh-creates-no-symlinks.md
@@ -1,4 +1,5 @@
 ---
+topic: building it
 status: accepted
 date: 2026-08-23
 deciders: jochen
diff --git a/02-DECISIONS/0013-schema-changes-are-numbered-migrations.md b/02-DECISIONS/0013-schema-changes-are-numbered-migrations.md
index 8f42d2e..cb7519e 100644
--- a/02-DECISIONS/0013-schema-changes-are-numbered-migrations.md
+++ b/02-DECISIONS/0013-schema-changes-are-numbered-migrations.md
@@ -1,4 +1,5 @@
 ---
+topic: building it
 status: accepted
 date: 2026-05-14
 deciders: jochen
diff --git a/02-DECISIONS/0014-no-npm-workspace.md b/02-DECISIONS/0014-no-npm-workspace.md
index 8914acb..1140d37 100644
--- a/02-DECISIONS/0014-no-npm-workspace.md
+++ b/02-DECISIONS/0014-no-npm-workspace.md
@@ -1,4 +1,5 @@
 ---
+topic: building it
 status: accepted
 date: 2026-06-04
 deciders: jochen
diff --git a/02-DECISIONS/0015-applications-live-in-their-own-repository.md b/02-DECISIONS/0015-applications-live-in-their-own-repository.md
index 565fb55..8ad1396 100644
--- a/02-DECISIONS/0015-applications-live-in-their-own-repository.md
+++ b/02-DECISIONS/0015-applications-live-in-their-own-repository.md
@@ -1,4 +1,5 @@
 ---
+topic: building it
 status: accepted
 date: 2026-07-10
 deciders: jochen
diff --git a/02-DECISIONS/0016-the-lab.md b/02-DECISIONS/0016-the-lab.md
index 4de914d..4b0b6b0 100644
--- a/02-DECISIONS/0016-the-lab.md
+++ b/02-DECISIONS/0016-the-lab.md
@@ -1,4 +1,5 @@
 ---
+topic: building it
 status: accepted
 date: 2026-08-28
 deciders: jochen
diff --git a/02-DECISIONS/0017-a-test-defends-a-decision.md b/02-DECISIONS/0017-a-test-defends-a-decision.md
index d2e43de..57ce326 100644
--- a/02-DECISIONS/0017-a-test-defends-a-decision.md
+++ b/02-DECISIONS/0017-a-test-defends-a-decision.md
@@ -1,4 +1,5 @@
 ---
+topic: checking it
 status: accepted
 date: 2026-08-24
 deciders: jochen
diff --git a/02-DECISIONS/0018-a-picture-is-read-from-what-runs.md b/02-DECISIONS/0018-a-picture-is-read-from-what-runs.md
index 7871c7a..04d9d32 100644
--- a/02-DECISIONS/0018-a-picture-is-read-from-what-runs.md
+++ b/02-DECISIONS/0018-a-picture-is-read-from-what-runs.md
@@ -1,4 +1,5 @@
 ---
+topic: checking it
 status: accepted
 date: 2026-08-24
 deciders: jochen
diff --git a/02-DECISIONS/0019-how-this-repository-works.md b/02-DECISIONS/0019-how-this-repository-works.md
index 385eec4..56cf26c 100644
--- a/02-DECISIONS/0019-how-this-repository-works.md
+++ b/02-DECISIONS/0019-how-this-repository-works.md
@@ -1,4 +1,5 @@
 ---
+topic: how we work
 status: accepted
 date: 2026-08-28
 deciders: jochen
@@ -77,11 +78,25 @@ settled. Everything else belongs in the design document, where the reasoning is
 **There is no ledger** — no separate document summarising, ranking or tracking decisions. A
 chronological view is generated from frontmatter, which is what a ledger was actually for.
 
-**The numbering is the flow here too.** Records are ordered the way somebody would learn the
-system — what the mesh is, then its tiers from the bottom up, then what runs on them and how it
-gets there, then how it is built, how it is checked, and how we work. **Not chronologically**: the
-date is in the frontmatter and a consolidated record holds decisions taken across a week, so
-ordering by age would order by an accident that no longer exists.
+**A number identifies a record and never changes.** It is not a position, and it cannot be
+both — a position moves when the set changes, and an identity that moves is not one.
+
+That is not a preference. Records are referenced from **outside** this repository: code
+comments, commit messages, the knowledge base. Renumbering once cost 96 references across two
+code repositories, and nothing in either would have failed to compile — the comments would
+simply have pointed at the wrong reasoning, which is worse than a broken link because nothing
+reports it.
+
+**So the reading order lives in a generated index**, from each record's `topic:` — what the mesh
+is, then its tiers from the bottom up, then what runs on them and how it gets there, then how it
+is built, how it is checked, and how we work.
+
+**And the index is written, not only generated on demand.** A reader looking at the folder on a
+forge sees the folder, not a command. The objection to a written index is that it drifts, and
+that is answered by **checking** it rather than by refusing to write one — which is §5's own
+rule: a rule states how it is checked. A record with no topic, or a topic nobody defined, fails
+the same check, because the quiet failure is a record that vanishes from the order rather than
+appearing in the wrong place.
 
 **The design layer is what you read.** These records explain *why* a thing is as it is. They are
 not a description of the system, and needing to read them to understand it would mean the design
diff --git a/02-DECISIONS/0020-the-mesh-is-governed-by-a-constitution.md b/02-DECISIONS/0020-the-mesh-is-governed-by-a-constitution.md
index 3e199c6..c43cbdd 100644
--- a/02-DECISIONS/0020-the-mesh-is-governed-by-a-constitution.md
+++ b/02-DECISIONS/0020-the-mesh-is-governed-by-a-constitution.md
@@ -1,4 +1,5 @@
 ---
+topic: how we work
 status: accepted
 date: 2026-07-10
 deciders: jochen
diff --git a/02-DECISIONS/0021-hq-is-the-source-of-the-constitution.md b/02-DECISIONS/0021-hq-is-the-source-of-the-constitution.md
index 82c4ec5..9317c7a 100644
--- a/02-DECISIONS/0021-hq-is-the-source-of-the-constitution.md
+++ b/02-DECISIONS/0021-hq-is-the-source-of-the-constitution.md
@@ -1,4 +1,5 @@
 ---
+topic: how we work
 status: accepted
 date: 2026-08-23
 deciders: jochen
diff --git a/02-DECISIONS/0022-the-constitution-absorbs-what-is-enforced.md b/02-DECISIONS/0022-the-constitution-absorbs-what-is-enforced.md
index 25506f6..7b7a608 100644
--- a/02-DECISIONS/0022-the-constitution-absorbs-what-is-enforced.md
+++ b/02-DECISIONS/0022-the-constitution-absorbs-what-is-enforced.md
@@ -1,4 +1,5 @@
 ---
+topic: how we work
 status: accepted
 date: 2026-08-26
 deciders: jochen
diff --git a/02-DECISIONS/0023-approval-is-the-checkpoint.md b/02-DECISIONS/0023-approval-is-the-checkpoint.md
index 80ae446..2ec3fad 100644
--- a/02-DECISIONS/0023-approval-is-the-checkpoint.md
+++ b/02-DECISIONS/0023-approval-is-the-checkpoint.md
@@ -1,4 +1,5 @@
 ---
+topic: how we work
 status: accepted
 date: 2026-08-26
 deciders: jochen
diff --git a/02-DECISIONS/README.md b/02-DECISIONS/README.md
index fee22e0..b3a5767 100644
--- a/02-DECISIONS/README.md
+++ b/02-DECISIONS/README.md
@@ -62,6 +62,62 @@ rather than guessing.
 
 ## Index
 
-The index is **generated, not maintained** — run the `hq-status` skill, which reads the
-frontmatter of every record. A hand-written index drifts from the folder it describes, and
-this one had already done so after a single addition.
+**A number identifies a record and never changes.** Records are referenced from outside this
+repository — code comments, commit messages — so a number that moves invalidates them silently.
+Renumbering once cost 96 references across two code repositories, and that is why the numbers
+are now fixed.
+
+So the folder is in creation order, and **the reading order lives here.** It is generated from
+each record's `topic:` and written, because a reader looking at the folder on a forge sees the
+folder rather than a command. The objection to a written index is that it drifts — which is
+answered by checking it rather than by refusing to write one:
+
+```
+python3 00-META/checks/index.py --write    regenerate
+python3 00-META/checks/index.py            fail if stale
+```
+
+<!-- index:start -->
+
+### What the mesh is
+
+- **0001** — [The mesh brokers capabilities; nodes host; agents think](0001-mesh-brokers-nodes-host-agents-think.md)
+- **0002** — [Nodes communicate over a message broker, not over HTTP](0002-nodes-communicate-over-a-broker.md)
+- **0003** — [An agent is a persistent employee, not an instance of a pool](0003-agents-are-persistent-employees.md)
+
+### Its tiers, from the bottom up
+
+- **0004** — [A node, and how it joins](0004-a-node-and-how-it-joins.md)
+- **0005** — [The node host](0005-the-node-host.md)
+- **0006** — [The substrate and the control plane](0006-the-substrate-and-the-control-plane.md)
+- **0007** — [Connectivity](0007-connectivity.md)
+- **0008** — [A context owns its store, exclusively](0008-a-context-owns-its-store.md)
+
+### What runs on them, and how it gets there
+
+- **0009** — [Modules and the graph](0009-modules-and-the-graph.md)
+- **0010** — [Delivery](0010-delivery.md)
+
+### How it is built
+
+- **0011** — [Managed files are generated onto nodes and never edited there](0011-managed-files-are-generated-never-edited.md)
+- **0012** — [The mesh creates no symlinks — a derived file is a copy](0012-the-mesh-creates-no-symlinks.md)
+- **0013** — [Schema and state changes are numbered migrations, in the same language as the code](0013-schema-changes-are-numbered-migrations.md)
+- **0014** — [No workspace — each module is a standalone package consuming published dependencies](0014-no-npm-workspace.md)
+- **0015** — [Applications live in their own repository; the monorepo is for the mesh](0015-applications-live-in-their-own-repository.md)
+- **0016** — [The lab](0016-the-lab.md)
+
+### How it is checked
+
+- **0017** — [A test defends a decision](0017-a-test-defends-a-decision.md)
+- **0018** — [A picture of a system is read from the system, never from what asked for it](0018-a-picture-is-read-from-what-runs.md)
+
+### How we work
+
+- **0019** — [How this repository works](0019-how-this-repository-works.md)
+- **0020** — [The mesh is governed by a constitution, injected where work is decided](0020-the-mesh-is-governed-by-a-constitution.md)
+- **0021** — [HQ is the source of the mesh constitution](0021-hq-is-the-source-of-the-constitution.md)
+- **0022** — [The constitution absorbs what is already enforced](0022-the-constitution-absorbs-what-is-enforced.md)
+- **0023** — [The approval is the checkpoint, not the second pair of hands](0023-approval-is-the-checkpoint.md)
+
+<!-- index:end -->