What causes "failed to load module from type defs json: %w" in dagger/dagger?

Read the wrapped cause for the underlying module load error.

failed to load module from type defs json: %w

Error message

failed to load module from type defs json: %w

What it means

Wraps a failure to load the *core.Module object from the dagql ID derived from the typedefs JSON (dagql.NewID[*core.Module](modCallID).Load). Dagger throws this when the module produced by the SDK's moduleTypes exec cannot be resolved as a Module object in the current DAG session.

Source

Thrown at core/sdk/module_typedefs.go:158

			Field: "contents",
		},
	)
	if err != nil {
		return inst, fmt.Errorf("failed to get type defs json during module sdk codegen: %w", err)
	}

	var modID core.ModuleID
	if err = json.Unmarshal([]byte(modDefsID), &modID); err != nil {
		return inst, fmt.Errorf("failed to decode module ID from type defs json: %w", err)
	}

	modCallID, err := modID.ID()
	if err != nil {
		return inst, fmt.Errorf("failed to get module ID handle from type defs json: %w", err)
	}
	inst, err = dagql.NewID[*core.Module](modCallID).Load(ctx, dag)
	if err != nil {
		return inst, fmt.Errorf("failed to load module from type defs json: %w", err)
	}
	if modCallID.IsHandle() {
		cache, err := dagql.EngineCache(ctx)
		if err != nil {
			return inst, fmt.Errorf("failed to get engine cache for sdk moduleTypes dependency: %w", err)
		}
		if err := cache.AddExplicitDependency(ctx, ctr, inst, "sdk_module_types_generated_module"); err != nil {
			return inst, fmt.Errorf("failed to retain loaded module result from sdk moduleTypes exec: %w", err)
		}
	}

	return inst, nil
}

View on GitHub (pinned to 82ba2681db)

Solutions

Read the wrapped cause for the underlying module load error.
Retry the operation; check for engine/session restarts in logs.
Verify dependency modules resolve correctly and versions match.

Defensive patterns

Strategy: retry

Try / catch

inst, err := dagql.NewID[*core.Module](modCallID).Load(ctx, dag)
if err != nil {
    // check for session/engine restart; retry once
    return retryLoad(ctx, modCallID)
}

Prevention

Avoid engine restarts during module dependency loads
Keep dependency modules resolvable
Watch for context cancellation in long operations

When it happens

Trigger: The Load of the module ID errors: the referenced module result was computed in an inaccessible scope, the ID's underlying call failed, or session/engine state no longer has the result.

Common situations: Dependency module scoping issues (module loaded across scoped sessions); engine restart mid-operation; upstream module call that produced the ID failed.

Related errors

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/4da3ca44e0c2fca3. Report an issue: GitHub.