From e049b398ef6e08c2fb78988f0e00a6d88b641f06 Mon Sep 17 00:00:00 2001
From: Andrew Halberstadt <ahal@mozilla.com>
Date: Wed, 7 Oct 2026 16:24:21 -0400
Subject: [PATCH] fix: ensure 'github-issue-comment' tasks use PR cache
 namespaces

---
 src/taskgraph/util/cached_tasks.py | 16 ++++++++++++----
 test/test_util_cached_tasks.py     | 15 +++++++++++++++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/taskgraph/util/cached_tasks.py b/src/taskgraph/util/cached_tasks.py
index 5c050745b..525ba880f 100644
--- a/src/taskgraph/util/cached_tasks.py
+++ b/src/taskgraph/util/cached_tasks.py
@@ -63,9 +63,14 @@ def add_optimization(
     # Pull requests use a different target cache index route. This way we can
     # be confident they won't be used by anything other than the pull request
     # that created the cache in the first place.
-    if config.params["tasks_for"] == "github-pull-request" and config.graph_config[
-        "taskgraph"
-    ].get("cache-pull-requests", True):
+    #
+    # Comments on a pull request run against the PR's head, so they use the
+    # same cache namespace as the PR itself.
+    tasks_for = config.params["tasks_for"]
+    if tasks_for in (
+        "github-pull-request",
+        "github-issue-comment",
+    ) and config.graph_config["taskgraph"].get("cache-pull-requests", True):
         subs["head_ref"] = config.params["head_ref"]
         if subs["head_ref"].startswith("refs/heads/"):
             subs["head_ref"] = subs["head_ref"][11:]
@@ -76,7 +81,10 @@ def add_optimization(
     # ... and cache at the lowest level.
     subs["level"] = config.params["level"]
 
-    if config.params["tasks_for"].startswith("github-pull-request"):
+    if (
+        tasks_for.startswith("github-pull-request")
+        or tasks_for == "github-issue-comment"
+    ):
         if config.graph_config["taskgraph"].get("cache-pull-requests", True):
             taskdesc.setdefault("routes", []).append(
                 f"index.{TARGET_PR_CACHE_INDEX.format(**subs)}"
diff --git a/test/test_util_cached_tasks.py b/test/test_util_cached_tasks.py
index 3ab2fa67f..a07a56d1c 100644
--- a/test/test_util_cached_tasks.py
+++ b/test/test_util_cached_tasks.py
@@ -107,6 +107,10 @@ def assert_pull_request_nocache(task):
     }
 
 
+def assert_issue_comment(task):
+    assert_pull_request(task)
+
+
 @pytest.mark.parametrize(
     "extra_params,extra_graph_config,digest,digest_data",
     (
@@ -176,6 +180,17 @@ def assert_pull_request_nocache(task):
             None,
             id="pull_request_nocache",
         ),
+        pytest.param(
+            # extra_params
+            {"tasks_for": "github-issue-comment"},
+            # extra_graph_config
+            None,
+            # digest
+            "abc",
+            # digest_data
+            None,
+            id="issue_comment",
+        ),
     ),
 )
 def test_add_optimization(