diff --git a/e2e/harness/harness.go b/e2e/harness/harness.go
index ea715192..48e991d7 100644
--- a/e2e/harness/harness.go
+++ b/e2e/harness/harness.go
@@ -383,7 +383,9 @@ func generateStubWorkflow(name, scenarioTag string) string {
 	// generator discovers them and threads the matching preflight outputs through
 	// each deploy's with: block. image_tag drives the source_image_tag passthrough
 	// and image_digest drives the source_image_digest passthrough in the generated
-	// promote workflow.
+	// promote workflow. dry_run is declared so that deploys with supports_dry_run
+	// enabled receive the null-safe passthrough from the orchestrate workflow.
+	// Declaring it here is harmless for callbacks that do not use it.
 	return fmt.Sprintf(`name: %s
 on:
   workflow_call:
@@ -400,6 +402,9 @@ on:
       image_digest:
         required: false
         type: string
+      dry_run:
+        required: false
+        type: boolean
 jobs:
   %s:
     runs-on: ubuntu-latest
diff --git a/e2e/harness/scenario.go b/e2e/harness/scenario.go
index c20a7526..e5138ece 100644
--- a/e2e/harness/scenario.go
+++ b/e2e/harness/scenario.go
@@ -112,6 +112,7 @@ type DeployConfig struct {
 	DependsOn         []string          `yaml:"depends_on"`
 	OptionalDependsOn []string          `yaml:"optional_depends_on,omitempty"`
 	TimeoutMinutes    int               `yaml:"timeout_minutes,omitempty"`
+	SupportsDryRun    bool              `yaml:"supports_dry_run,omitempty"`
 	RunsOn            any               `yaml:"runs_on,omitempty"`
 	Permissions       map[string]string `yaml:"permissions,omitempty"`
 	Concurrency       *ConcurrencySpec  `yaml:"concurrency,omitempty"`
diff --git a/e2e/scenarios/orchestrate/dry-run-input-expression.yaml b/e2e/scenarios/orchestrate/dry-run-input-expression.yaml
new file mode 100644
index 00000000..e5ead247
--- /dev/null
+++ b/e2e/scenarios/orchestrate/dry-run-input-expression.yaml
@@ -0,0 +1,47 @@
+name: "Dry-Run Passthrough Uses Null-Safe Expression"
+description: |
+  Verifies that the generator emits the null-safe github.event.inputs.dry_run
+  accessor when a deploy callback has supports_dry_run: true.
+
+  The orchestrate workflow is triggered by push, schedule, and workflow_run
+  events -- none of which populate the inputs context. A bare inputs.dry_run
+  expression renders as an empty string on those triggers, which breaks the
+  boolean dispatch to the reusable callback workflow. The generator must use
+  github.event.inputs.dry_run instead so the value is null (and the boolean
+  coercion to false) rather than an empty string that fails type validation.
+
+  Generator-output verification scenario; the assertion runs on the staged repo
+  after StageRepoFromConfig generates workflows but before any orchestrate run,
+  so Docker and act are not required to validate the generated YAML.
+
+config:
+  trunk_branch: main
+  environments: ["dev", "prod"]
+  builds:
+    - name: app
+      workflow: build-app.yaml
+      triggers: ["src/**"]
+  deploys:
+    - name: app
+      workflow: deploy-app.yaml
+      triggers: []
+      supports_dry_run: true
+
+steps:
+  - name: "Initial commit; assert dry_run passthrough uses null-safe accessor"
+    action: commit
+    commit:
+      message: "feat: add app build and deploy with dry-run support"
+      files:
+        src/main.go: |
+          package main
+          func main() {}
+    expect:
+      workflow_files:
+        - path: ".github/workflows/orchestrate.yaml"
+          contains:
+            # The null-safe accessor works across push, schedule, and workflow_run triggers.
+            - "dry_run: ${{ github.event.inputs.dry_run }}"
+          not_contains:
+            # The bare inputs accessor renders empty on non-dispatch triggers and must not appear.
+            - "dry_run: ${{ inputs.dry_run }}"
diff --git a/internal/generate/dry_run_test.go b/internal/generate/dry_run_test.go
index 39fa2f7a..4c36c4b3 100644
--- a/internal/generate/dry_run_test.go
+++ b/internal/generate/dry_run_test.go
@@ -175,9 +175,12 @@ on:
 	content, err := gen.Generate()
 	require.NoError(t, err)
 
-	// dry_run must be forwarded in the with: block to the deploy job.
+	// dry_run must be forwarded in the with: block to the deploy job using the
+	// null-safe github.event.inputs accessor. The bare inputs.dry_run form renders
+	// empty on push/schedule/workflow_run, which is invalid for a boolean callback
+	// input and fails the reusable-workflow dispatch.
 	assert.Contains(t, content,
-		"dry_run: ${{ inputs.dry_run }}",
+		"dry_run: ${{ github.event.inputs.dry_run }}",
 		"orchestrate generator must pass dry_run to a supports_dry_run callback")
 }
 
@@ -219,7 +222,7 @@ on:
 
 	deploySection := extractJobSection(t, content, "deploy-app:")
 	assert.NotContains(t, deploySection,
-		"dry_run: ${{ inputs.dry_run }}",
+		"dry_run: ${{ github.event.inputs.dry_run }}",
 		"non-supports_dry_run callback must not receive dry_run in orchestrate")
 }
 
diff --git a/internal/generate/generator.go b/internal/generate/generator.go
index 91fbd02b..60f6131c 100644
--- a/internal/generate/generator.go
+++ b/internal/generate/generator.go
@@ -1091,8 +1091,15 @@ func (g *Generator) writeWithInputs(sb *strings.Builder, info CallbackInfo) {
 
 	// When a callback opts in to dry-run emulation, pass the dry_run dispatch
 	// input through so the callback can emulate internally instead of being skipped.
+	// Use github.event.inputs.dry_run rather than the bare inputs.dry_run context:
+	// orchestrate is triggered by push/schedule/workflow_run as well as dispatch,
+	// and on the non-dispatch events the inputs context is null so ${{ inputs.dry_run }}
+	// renders empty. Passing "" into a callback's boolean dry_run input fails the
+	// reusable-workflow dispatch. The github.event.inputs accessor is null-safe on
+	// those events (the callback falls back to its dry_run default), and on dispatch
+	// it still forwards the operator's value.
 	if info.SupportsDryRun {
-		inputs = append(inputs, "      dry_run: ${{ inputs.dry_run }}")
+		inputs = append(inputs, "      dry_run: ${{ github.event.inputs.dry_run }}")
 	}
 
 	// For build callbacks with a matrix, pass each dimension's current value to