fix(#397): replace O(N²) GetMicroflow/GetNanoflow with direct unit lookup

Lint rules that call GetMicroflow(id) inside a catalog microflow loop
were triggering N full ListMicroflows() scans — one per iteration — each
re-parsing all microflow BSON from the MPR database.  On large projects
this caused mxcli report to hang indefinitely.

Add getUnitByID(): V1 does a single-row SQLite query by BLOB primary key,
V2 uses the existing unit cache then reads one mxunit file.  Both paths
are effectively O(1) vs the previous O(N) full scan, making the overall
lint pass O(N) instead of O(N²).

Affected rules: ValidationFeedback, OverlappingActivities, NoCommitInLoop,
ExclusiveSplitCaption, ErrorHandlingOnCalls, NoContinueErrorHandling.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

sdk/mpr/reader_documents.go

@@ -201,19 +201,16 @@ func (r *Reader) ListMicroflows() ([]*microflows.Microflow, error) {
 }
 
 // GetMicroflow retrieves a microflow by ID.
+// Uses a direct unit lookup (O(1) for V1, O(cache) for V2) instead of loading all microflows.
 func (r *Reader) GetMicroflow(id model.ID) (*microflows.Microflow, error) {
-	microflowsList, err := r.ListMicroflows()
+	unit, err := r.getUnitByID(string(id))
 	if err != nil {
 		return nil, err
 	}
-
-	for _, mf := range microflowsList {
-		if mf.ID == id {
-			return mf, nil
-		}
+	if unit == nil {
+		return nil, fmt.Errorf("microflow not found: %s", id)
 	}
-
-	return nil, fmt.Errorf("microflow not found: %s", id)
+	return r.parseMicroflow(unit.ID, unit.ContainerID, unit.Contents)
 }
 
 // IsRule reports whether the given qualified name refers to a rule
@@ -285,19 +282,16 @@ func (r *Reader) ListNanoflows() ([]*microflows.Nanoflow, error) {
 }
 
 // GetNanoflow retrieves a nanoflow by ID.
+// Uses a direct unit lookup (O(1) for V1, O(cache) for V2) instead of loading all nanoflows.
 func (r *Reader) GetNanoflow(id model.ID) (*microflows.Nanoflow, error) {
-	nanoflows, err := r.ListNanoflows()
+	unit, err := r.getUnitByID(string(id))
 	if err != nil {
 		return nil, err
 	}
-
-	for _, nf := range nanoflows {
-		if nf.ID == id {
-			return nf, nil
-		}
+	if unit == nil {
+		return nil, fmt.Errorf("nanoflow not found: %s", id)
 	}
-
-	return nil, fmt.Errorf("nanoflow not found: %s", id)
+	return r.parseNanoflow(unit.ID, unit.ContainerID, unit.Contents)
 }
 
 // ListPages returns all pages in the project.

sdk/mpr/reader_units.go

@@ -4,11 +4,14 @@
 package mpr
 
 import (
+	"database/sql"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
 
+	"github.com/mendixlabs/mxcli/mdl/types"
 	"go.mongodb.org/mongo-driver/bson"
 )
 
@@ -587,3 +590,64 @@ func (r *Reader) ListRawUnits(objectType string) ([]*RawUnitInfo, error) {
 
 	return result, nil
 }
+
+// getUnitByID fetches a single rawUnit by its UUID string without loading all units.
+// Returns (nil, nil) when the ID is not found.
+// V1: direct SQLite BLOB lookup — O(1). V2: cache lookup + single file read — O(cache size).
+func (r *Reader) getUnitByID(id string) (*rawUnit, error) {
+	if r.version == MPRVersionV2 {
+		return r.getUnitByIDV2(id)
+	}
+	return r.getUnitByIDV1(id)
+}
+
+func (r *Reader) getUnitByIDV1(id string) (*rawUnit, error) {
+	blob := types.UUIDToBlob(id)
+	if blob == nil {
+		return nil, fmt.Errorf("invalid unit ID: %s", id)
+	}
+	row := r.db.QueryRow(
+		"SELECT UnitID, ContainerID, ContainmentName, Contents FROM Unit WHERE UnitID = ?",
+		blob,
+	)
+	var unitID, containerID []byte
+	var containmentName string
+	var contents []byte
+	if err := row.Scan(&unitID, &containerID, &containmentName, &contents); err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("failed to query unit %s: %w", id, err)
+	}
+	return &rawUnit{
+		ID:              blobToUUID(unitID),
+		ContainerID:     blobToUUID(containerID),
+		ContainmentName: containmentName,
+		Type:            getTypeFromContents(contents),
+		Contents:        contents,
+	}, nil
+}
+
+func (r *Reader) getUnitByIDV2(id string) (*rawUnit, error) {
+	if !r.unitCacheValid {
+		if err := r.buildUnitCache(); err != nil {
+			return nil, err
+		}
+	}
+	for _, cu := range r.unitCache {
+		if cu.ID == id {
+			contents, err := r.readMprContents(id)
+			if err != nil {
+				return nil, err
+			}
+			return &rawUnit{
+				ID:              cu.ID,
+				ContainerID:     cu.ContainerID,
+				ContainmentName: cu.ContainmentName,
+				Type:            cu.Type,
+				Contents:        contents,
+			}, nil
+		}
+	}
+	return nil, nil
+}