fix(actions): resolve pull_request_target reusable workflows at the base commit (#38886)

For a `pull_request_target` (PRT) run, Gitea loads the top-level
workflow from the trusted base branch, but any local reusable workflow
it calls (`uses: ./...`) was read from the PR **head** commit, which the
fork author controls.

## Fix

**Record the source commit where the content is read.**
`DetectedWorkflow` now carries a `SourceCommitSHA` filled in next to
`Content`, so the PRT detection pass at the base commit records the base
SHA automatically.

**Defense in depth.** `loadReusableWorkflowSource` pins the PR base
commit for a PRT run's local `uses: ./...` rather than trusting the
stored SHA. This also covers runs recorded before this change, whose
rows still hold the head SHA and would otherwise resolve from the fork
on rerun.

Existing run rows are not migrated.

---------

Co-authored-by: Zettat <zettat123@gmail.com>

modules/actions/scoped_workflows.go

@@ -62,6 +62,7 @@ func ParseScopedWorkflows(ctx context.Context, gitRepo *git.Repository, sourceCo
 func MatchScopedWorkflows(
 	ctx context.Context,
 	parsed []*ParsedScopedWorkflow,
+	sourceCommitSHA string,
 	consumerGitRepo *git.Repository,
 	consumerCommit *git.Commit,
 	inputEvent webhook_module.HookEventType,
@@ -74,9 +75,10 @@ func MatchScopedWorkflows(
 				continue
 			}
 			dwf := &DetectedWorkflow{
-				EntryName:    p.EntryName,
-				TriggerEvent: evt,
-				Content:      p.Content,
+				EntryName:       p.EntryName,
+				TriggerEvent:    evt,
+				Content:         p.Content,
+				SourceCommitSHA: sourceCommitSHA,
 			}
 			switch detectWorkflowMatch(ctx, consumerGitRepo, consumerCommit, inputEvent, payload, evt) {
 			case detectMatched:

modules/actions/workflows.go

@@ -29,6 +29,8 @@ type DetectedWorkflow struct {
 	EntryName    string
 	TriggerEvent *jobparser.Event
 	Content      []byte
+	// SourceCommitSHA is the commit Content was read from, and must always be filled in together with Content.
+	SourceCommitSHA string
 }
 
 type detectResult int
@@ -205,17 +207,19 @@ func DetectWorkflows(
 			if evt.IsSchedule() {
 				if detectSchedule {
 					dwf := &DetectedWorkflow{
-						EntryName:    entry.Name(),
-						TriggerEvent: evt,
-						Content:      content,
+						EntryName:       entry.Name(),
+						TriggerEvent:    evt,
+						Content:         content,
+						SourceCommitSHA: commit.ID.String(),
 					}
 					schedules = append(schedules, dwf)
 				}
 			} else {
 				dwf := &DetectedWorkflow{
-					EntryName:    entry.Name(),
-					TriggerEvent: evt,
-					Content:      content,
+					EntryName:       entry.Name(),
+					TriggerEvent:    evt,
+					Content:         content,
+					SourceCommitSHA: commit.ID.String(),
 				}
 				switch detectWorkflowMatch(ctx, gitRepo, commit, triggedEvent, payload, evt) {
 				case detectMatched:
@@ -254,9 +258,10 @@ func DetectScheduledWorkflows(ctx context.Context, gitRepo *git.Repository, comm
 			if evt.IsSchedule() {
 				log.Trace("detect scheduled workflow: %q", entry.Name())
 				dwf := &DetectedWorkflow{
-					EntryName:    entry.Name(),
-					TriggerEvent: evt,
-					Content:      content,
+					EntryName:       entry.Name(),
+					TriggerEvent:    evt,
+					Content:         content,
+					SourceCommitSHA: commit.ID.String(),
 				}
 				wfs = append(wfs, dwf)
 			}