diff --git a/.github/workflows/validate.yml b/.github/workflows/validate.yml
index 671f9c38..06fe7e5f 100644
--- a/.github/workflows/validate.yml
+++ b/.github/workflows/validate.yml
@@ -37,8 +37,9 @@ jobs:
           BEFORE_SHA: ${{ github.event.before }}
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.sha }}
-          DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
+          DEVELOPMENT_BRANCH: dev
         run: |
+          git fetch -q origin "refs/heads/$DEVELOPMENT_BRANCH:refs/remotes/origin/$DEVELOPMENT_BRANCH"
           node scripts/validate-commit-provenance.mjs --check-hook-mode --github-range
 
   # Догоняющая проверка процесса (PROCESS.md §10.3). Хуки ловят нарушение на
@@ -59,11 +60,12 @@ jobs:
           BEFORE_SHA: ${{ github.event.before }}
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.sha }}
-          DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
+          DEVELOPMENT_BRANCH: dev
           TARGET_REF: ${{ github.ref }}
           # Публичный репозиторий: штатного токена хватает на чтение issue.
           GH_TOKEN: ${{ github.token }}
         run: |
+          git fetch -q origin "refs/heads/$DEVELOPMENT_BRANCH:refs/remotes/origin/$DEVELOPMENT_BRANCH"
           node scripts/process-gate.mjs --github-range --issues
 
   # Классификация изменённых путей: тяжёлые job идут только там, где менялось
diff --git a/scripts/process-gate.mjs b/scripts/process-gate.mjs
index 8e024840..07cbed88 100644
--- a/scripts/process-gate.mjs
+++ b/scripts/process-gate.mjs
@@ -425,7 +425,7 @@ function main(argv) {
       beforeSha: process.env.BEFORE_SHA,
       baseSha: process.env.BASE_SHA,
       headSha: process.env.HEAD_SHA,
-      defaultBranch: process.env.DEFAULT_BRANCH,
+      developmentBranch: process.env.DEVELOPMENT_BRANCH,
     }, (args) => git(args, repo).trim());
   }
   if (!range) {
diff --git a/scripts/validate-commit-provenance.mjs b/scripts/validate-commit-provenance.mjs
index db7ef5d7..f010bba5 100644
--- a/scripts/validate-commit-provenance.mjs
+++ b/scripts/validate-commit-provenance.mjs
@@ -79,7 +79,7 @@ function gitObjectExists(revision, runner = git) {
 }
 
 export function resolveValidationRange({
-  eventName, beforeSha, baseSha, headSha, defaultBranch,
+  eventName, beforeSha, baseSha, headSha, developmentBranch = 'dev',
 }, runner = git) {
   if (!headSha) throw new Error('HEAD_SHA is required');
   if (eventName === 'pull_request') {
@@ -90,7 +90,11 @@ export function resolveValidationRange({
     && gitObjectExists(beforeSha, runner);
   const comparison = hasBefore
     ? beforeSha
-    : `refs/remotes/origin/${defaultBranch || 'main'}`;
+    // A first push has an all-zero `before`. Issue branches are cut from the
+    // integration branch, not GitHub's default branch (`main`), so comparing
+    // with main would pull already-landed dev commits into the validation
+    // range and judge unrelated/closed issues again (#165).
+    : `refs/remotes/origin/${developmentBranch || 'dev'}`;
   return `${runner(['merge-base', comparison, headSha])}..${headSha}`;
 }
 
@@ -129,7 +133,7 @@ function main(argv) {
           beforeSha: process.env.BEFORE_SHA,
           baseSha: process.env.BASE_SHA,
           headSha: process.env.HEAD_SHA,
-          defaultBranch: process.env.DEFAULT_BRANCH,
+          developmentBranch: process.env.DEVELOPMENT_BRANCH,
         })
       : argv[rangeAt + 1];
     if (!range) throw new Error('--range requires a git revision range');
diff --git a/test/commit-provenance.test.mjs b/test/commit-provenance.test.mjs
index 4248ba4c..5e3f8e39 100644
--- a/test/commit-provenance.test.mjs
+++ b/test/commit-provenance.test.mjs
@@ -39,7 +39,7 @@ test('hook mode requires the executable index bit', () => {
   );
 });
 
-test('validation range uses ancestry for PRs, normal pushes and new branches', () => {
+test('validation range uses PR ancestry, push before and dev for a new issue branch', () => {
   const calls = [];
   const runner = (args) => {
     calls.push(args);
@@ -50,11 +50,13 @@ test('validation range uses ancestry for PRs, normal pushes and new branches', (
   }, runner), 'common-base..head');
   assert.deepEqual(calls.at(-1), ['merge-base', 'base', 'head']);
   assert.equal(resolveValidationRange({
-    eventName: 'push', beforeSha: '000000', headSha: 'head', defaultBranch: 'main',
+    // GitHub's default branch is main, but House Plan issue branches start at
+    // dev. The all-zero first-push SHA must therefore compare with origin/dev.
+    eventName: 'push', beforeSha: '000000', headSha: 'head',
   }, runner), 'common-base..head');
-  assert.deepEqual(calls.at(-1), ['merge-base', 'refs/remotes/origin/main', 'head']);
+  assert.deepEqual(calls.at(-1), ['merge-base', 'refs/remotes/origin/dev', 'head']);
   assert.equal(resolveValidationRange({
-    eventName: 'push', beforeSha: 'before', headSha: 'head', defaultBranch: 'main',
+    eventName: 'push', beforeSha: 'before', headSha: 'head', developmentBranch: 'dev',
   }, runner), 'common-base..head');
   assert.deepEqual(calls.at(-1), ['merge-base', 'before', 'head']);
 });