fix(open-swe): restrict Linear token attribution to comment author only

Split actor_email (comment_author only, feeds github_login for token
attribution) from user_email (full fallback chain, for display/model).
This ensures a PR is never opened as a non-actor (creator/assignee).

Add test_resolve_github_token_linear_defaults_to_bot to lock the
security-critical default: Linear + mapped login + no opt-in → bot.

agent/webhooks/linear.py

@@ -40,12 +40,19 @@ async def process_linear_issue(  # noqa: PLR0912, PLR0915
     if not full_issue:
         full_issue = issue_data
 
-    user_email = None
     user_name = None
+    # Actor email for token attribution: restricted to the comment author only.
+    # The creator/assignee fallback chain is intentionally excluded here so a PR
+    # is never opened as a non-actor.
+    actor_email = None
     comment_author = issue_data.get("comment_author", {})
     if comment_author:
-        user_email = comment_author.get("email")
+        actor_email = comment_author.get("email")
         user_name = comment_author.get("name")
+
+    # User email with full fallback chain for display, model selection, and
+    # @mention instructions.
+    user_email = actor_email
     if not user_email:
         creator = full_issue.get("creator", {})
         if creator:
@@ -165,10 +172,11 @@ async def process_linear_issue(  # noqa: PLR0912, PLR0915
     )
     content_blocks: list[dict[str, Any]] = [create_text_block(prompt)]
 
-    # Resolve the GitHub login from the Linear email via the same user-mapping
-    # store Slack uses, so PRs open *as the triggering user* and the thread is
-    # tagged for the dashboard.
-    mapped_login = await webapp.resolve_login_from_email_async(user_email) if user_email else None
+    # Resolve the GitHub login from the actor's Linear email via the same
+    # user-mapping store Slack uses, so PRs open *as the triggering user* and the
+    # thread is tagged for the dashboard. Restricted to the comment author so
+    # token attribution never falls back to creator/assignee.
+    mapped_login = await webapp.resolve_login_from_email_async(actor_email) if actor_email else None
 
     image_model_override: tuple[str, str] | None = None
     if image_urls:

tests/test_auth_sources.py

@@ -234,6 +234,25 @@ def test_resolve_github_token_linear_optin_no_token_falls_back_to_bot_in_bot_onl
     assert (token, expires_at) == ("bot-tok", None)
 
 
+def test_resolve_github_token_linear_defaults_to_bot(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    # DEFAULT (no author_prs_as_user opt-in): linear runs author as the app bot,
+    # even when a valid per-user token and mapped login exist — so PRs can never
+    # be opened as a non-actor (creator/assignee).
+    _stub_dashboard_store(monkeypatch, token="user-tok")
+    _set_profile(monkeypatch, author_prs_as_user=False)
+    monkeypatch.setattr(auth, "is_bot_token_only_mode", lambda: False)
+
+    async def fake_bot(thread_id: str):
+        return ("bot-tok", None)
+
+    monkeypatch.setattr(auth, "_resolve_bot_installation_token", fake_bot)
+
+    token, _ = asyncio.run(auth.resolve_github_token(_linear_config(), "t1"))
+    assert token == "bot-tok"
+
+
 @pytest.mark.parametrize("source", ["github"])
 def test_resolve_github_token_bot_only_mode_non_slack_uses_bot(
     monkeypatch: pytest.MonkeyPatch, source: str