diff --git a/AGENTS.md b/AGENTS.md
index 3057b43..e74557b 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -36,6 +36,8 @@ Never start a long-lived / blocking process such as `npm run watch`. It runs unt
 
 `backlog.tasks` uses the vscode-todotasks format (not Markdown). A line ending in `:` is a project; every other line is a task. Status glyphs: `☐` open, `✔` done, `✘` cancelled; subtasks nest by indentation. Inline `@tags` carry metadata — `@done` / `@cancelled` mark completion, `@critical` / `@high` / `@low` / `@today` set priority. The `(…)` timestamp after `@done` is editor-generated: omit it when checking off by hand.
 
+**Required coupling:** a `✔` line _must_ also carry `@done`, and a `✘` line _must_ carry `@cancelled`. The `sandy081.todotasks` extension treats the glyph as the completion signal, then unconditionally searches for the matching tag to decorate; a bare `✔`/`✘` with no tag makes it compute an illegal `Range` (negative character offset) that throws and kills all highlighting/decoration for the document. A `☐` may stand alone. So check off by hand as `✔ … @done` (optionally `@done (timestamp)`), never a lone `✔`.
+
 ### Working on tasks
 
 - **Task with subtasks** (a task that has indented children): create a branch off `main` using the prefix inferred from the task content (`feature/…` / `fix/…` / `chore/…`), check it out, work on each subtask with commits, then present a concise handover for the user to review. Use this fixed shape:
diff --git a/backlog.tasks b/backlog.tasks
index 7a13c2b..108d5a7 100644
--- a/backlog.tasks
+++ b/backlog.tasks
@@ -9,8 +9,8 @@ Setup:
 ☐ Add gitea release page in CI @high
 ☐ Split off template into separate package => pi --session 01a07dde-7050-7054-bb36-1606d7eb2bc3 @high
 ✔ Document branching model @done
-    ✔ Describe branching model: when to branch, base branch, naming
-    ✔ Clarify release workflow: who pushes `main`, CI as post-merge gate, drop PR usage
+    ✔ Describe branching model: when to branch, base branch, naming @done
+    ✔ Clarify release workflow: who pushes `main`, CI as post-merge gate, drop PR usage @done (9/8/2026, 2:54:32 PM)
 
 v1.0:
 ☐ API surface is stable and fully typed