diff --git a/todo.md b/todo.md
index d20d293..c1c85d1 100644
--- a/todo.md
+++ b/todo.md
@@ -6,7 +6,7 @@
 
 `Bar = 0.1`
 
-`Next ID = 152`
+`Next ID = 153`
 
 ## Items
 
@@ -23,6 +23,7 @@
 | 133 | 0.3.0 |  | decision | **Write mentions, emoji, dates, statuses and inline cards as semantic HTML in `adfToHtml` and read them back in `htmlToAdf`, in place of the carry element.** | 2 | 2 | 2 | 4 | 4 | 6 by 3 | 3.0 |
 | 132 | 0.3.0 |  |  | **Write tables as `<table>` in `adfToHtml` and read them back in `htmlToAdf`, in place of the carry element.** | 2 | 2 | 2 | 4 | 5 | 6 by 4 | 2.4 |
 | 73 | 0.3.0 | 33, 91, 95, 109, 115, 132, 133, 145, 146, 150 |  | **Announce the package where someone needing an ADF converter already reads: JRACLOUD-77436, the Atlassian developer community and Stack Overflow's ADF-to-markdown questions.** | 1 | 2 | 2 | 3 | 2 | 3 by 8 | 16.9 |
+| 152 | 0.3.0 |  | owner | **Mutation-test a chunk's changed lines in 15 minutes or less, with one command the README documents.** | 3 | 2 | 1 | 4 | 4 | code health by 3 | 13.1 |
 | 72 | 0.3.0 | 33, 91, 95, 109, 115, 132, 133, 145, 146, 150 | decision | **Re-create `gitea.larvit.se/larvit/adf-codec` as a read-only pull mirror of GitHub, its issues and Actions off and its description pointing at GitHub.** | 1 | 2 | 1 | 2 | 1 | 3 by 1 | 2.5 |
 | 128 | 0.4.0 |  |  | **Pin the portable flavour's block reading and writing with tests: callout titles past one line, a link beside other marks in a title, the nesting limit of callouts and task lists, refusals inside tasks and their paths, and empty or non-paragraph tasks.** | 2 | 1 | 1 | 2 | 3 | code health by 3 | 19.6 |
 | 75 | 0.4.0 |  |  | **Make the generated-markdown property write block carries as `adf:` fences, canonical and hostile.** | 1 | 1 | 1 | 1 | 2 | code health by 2 | 17.4 |
@@ -170,6 +171,19 @@ solves it, then links the GitHub repository, the README's comparison table and t
 opening. The maintainer posts them once `0.3.0` is published (`docs/decisions.md` §Posts
 announcing a release wait for its publish). Found while planning discoverability, 2026-10-04.
 
+### 152. Mutation-test a chunk's changed lines in 15 minutes or less, with one command the README documents.
+
+Today each stability review sets Stryker up by hand, and a run takes from 25 minutes to 3 hours. In the week to 2026-10-28, the reviewers' test runs took 17 hours: more than every other test run in the project together. The gate itself is quick: `./ci.sh` takes about 1.8 minutes, and CI about 2.6.
+
+Ways to get there, to measure before choosing:
+
+- Check the Stryker config in, so no review rebuilds it.
+- Mutate only the lines the chunk changes, and run only the tests that cover each mutant (`coverageAnalysis: "perTest"`).
+- Run the property tests with fewer runs under mutation, through `PROPERTY_RUNS`.
+- Run the mutants on Node alone; Deno, Bun and Firefox stay in the gate.
+
+Done when a mutation run of a shipped chunk's changed lines, such as item 122's, finishes in 15 minutes or less under `~/.claude/bin/run-heavy`.
+
 ### 72. Re-create `gitea.larvit.se/larvit/adf-codec` as a read-only pull mirror of GitHub, its issues and Actions off and its description pointing at GitHub.
 
 Blocked by every other `0.3.0` item but 73 (the maintainer, 2026-10-05; moved to `0.3.0` 2026-10-28,