diff --git a/docs/rules/DEV-450.md b/docs/rules/DEV-450.md
new file mode 100644
index 0000000..8a63007
--- /dev/null
+++ b/docs/rules/DEV-450.md
@@ -0,0 +1,38 @@
+---
+id: DEV-450
+title: "Resolve Every Inline Thread With Its Answer"
+status: "active"
+enforcement: "manual"
+severity: "error"
+depends_on: ["DEV-365"]
+---
+
+## Problem
+
+A reviewer cannot tell whether the author fixed, answered, or ignored the
+comments on a merged PR. A real objection ships and nobody notices.
+
+## Solution
+
+Each inline thread is a question the reviewer asked. Only the author knows the
+answer, so the author writes it on the thread before closing it. Resolving marks
+the thread settled; the reply carries the answer.
+
+1. Reply to every inline thread before you merge, and name what changed. One
+   sentence is enough.
+1. Resolve the thread after you post that reply and push the fix.
+1. When you fixed it in another PR, the Problem, or a follow-up issue, say which
+   one and give its number.
+1. Reply and leave the thread open when you disagree. The reviewer decides, per
+   [DEV-410](./DEV-410.md).
+
+```md
+Good: fixed in 4a1c2f0, the heading is now `###`. [Resolve]
+Bad:  [Resolve]
+```
+
+### Acceptance Criteria
+
+- [ ] Every inline thread on the PR has a reply at merge
+- [ ] Each reply names what changed, or the PR or issue that carries the fix
+- [ ] Every thread still open at merge holds a stated disagreement
diff --git a/docs/rules/README.md b/docs/rules/README.md
index 8bd6bab..dd28c94 100644
--- a/docs/rules/README.md
+++ b/docs/rules/README.md
@@ -91,6 +91,7 @@ How to review, and the quality bar work is held to.
 - [DEV-420](./DEV-420.md): scout open PRs when idle
 - [DEV-430](./DEV-430.md): deliver bug-free work; review is a safety check
 - [DEV-440](./DEV-440.md): judge work by value delivered, not effort spent
+- [DEV-450](./DEV-450.md): resolve every inline thread with its answer
 
 ### 5. Advocacy