enforce gofmt formatting and add Fmt/FmtCheck mage targets

Run gofmt -w on 9 files that had minor alignment/whitespace drift
(pair.go, filter.go, ior_mode_registry.go, ior_mode_test.go,
runtime.go, engine.go, dashboard/model.go, flamegraph/model.go,
flamegraph/renderer.go).

Add two new Mage targets to Magefile.go:
- `mage fmt`      – rewrites all .go files in-place via go/format
- `mage fmtCheck` – dry-run check; fails with a list of offending
                    files, suitable as a CI gate

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

10 files changed, 77 insertions, 23 deletions

diff --git a/Magefile.go b/Magefile.go
index 6f24e9d..9d4261d 100644
--- a/Magefile.go
+++ b/Magefile.go
@@ -124,6 +124,63 @@ func TestRace() error {
 	return sh.RunWithV(goEnv(), "go", "test", "./...", "-race", "-failfast", "-timeout=90m")
 }
 
+// Fmt runs gofmt -w on all Go source files to enforce canonical formatting.
+func Fmt() error {
+	return fmtGoFiles(false)
+}
+
+// FmtCheck verifies that all Go source files are gofmt-formatted.
+// It exits with a non-zero status if any file needs reformatting,
+// making it suitable for use as a CI gate (e.g. mage fmtCheck).
+func FmtCheck() error {
+	return fmtGoFiles(true)
+}
+
+// fmtGoFiles walks the repo tree and either formats or checks every .go file.
+// When checkOnly is true, any file that needs reformatting is reported as an
+// error without writing to disk. When false, files are rewritten in place.
+func fmtGoFiles(checkOnly bool) error {
+	var unformatted []string
+	err := filepath.WalkDir(".", func(path string, d os.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		// Skip vendor and hidden directories (e.g. .git).
+		if d.IsDir() && (d.Name() == "vendor" || strings.HasPrefix(d.Name(), ".")) {
+			return filepath.SkipDir
+		}
+		if d.IsDir() || !strings.HasSuffix(path, ".go") {
+			return nil
+		}
+		src, err := os.ReadFile(path)
+		if err != nil {
+			return fmt.Errorf("read %s: %w", path, err)
+		}
+		formatted, err := format.Source(src)
+		if err != nil {
+			// Syntax errors are reported but don't abort the walk.
+			fmt.Printf("gofmt: syntax error in %s: %v\n", path, err)
+			return nil
+		}
+		if string(src) == string(formatted) {
+			return nil
+		}
+		if checkOnly {
+			unformatted = append(unformatted, path)
+			return nil
+		}
+		return os.WriteFile(path, formatted, d.Type().Perm())
+	})
+	if err != nil {
+		return err
+	}
+	if len(unformatted) > 0 {
+		return fmt.Errorf("gofmt: %d file(s) need formatting:\n  %s\nRun `mage fmt` to fix.",
+			len(unformatted), strings.Join(unformatted, "\n  "))
+	}
+	return nil
+}
+
 // TestWithName runs a specific test by name.
 func TestWithName() error {
 	mg.Deps(BpfBuild)
diff --git a/internal/event/pair.go b/internal/event/pair.go
index c31fd90..1626e88 100644
--- a/internal/event/pair.go
+++ b/internal/event/pair.go
@@ -25,7 +25,7 @@ type Pair struct {
 	Comm            string
 	Duration        uint64
 	DurationToPrev  uint64
-	Bytes          uint64 // Number of bytes transferred (read/write/transfer syscalls only)
+	Bytes           uint64 // Number of bytes transferred (read/write/transfer syscalls only)
 }
 
 func NewPair(enterEv Event) *Pair {
diff --git a/internal/globalfilter/filter.go b/internal/globalfilter/filter.go
index 01213aa..689a728 100644
--- a/internal/globalfilter/filter.go
+++ b/internal/globalfilter/filter.go
@@ -242,4 +242,3 @@ func sameFilter[T comparable](left, right *T) bool {
 		return *left == *right
 	}
 }
-
diff --git a/internal/ior_mode_registry.go b/internal/ior_mode_registry.go
index 3eb59b5..e262784 100644
--- a/internal/ior_mode_registry.go
+++ b/internal/ior_mode_registry.go
@@ -42,9 +42,9 @@ type runnerDeps struct {
 // defaultRunnerDeps returns the production function set.
 func defaultRunnerDeps() runnerDeps {
 	return runnerDeps{
-		getEUID:            os.Geteuid,
-		runTrace:           runTrace,
-		runParquet:         runHeadlessParquet,
+		getEUID:             os.Geteuid,
+		runTrace:            runTrace,
+		runParquet:          runHeadlessParquet,
 		runTraceWithContext: runTraceWithContext,
 		// TUI runners are nil until SetTUIRunners is called from cmd/ior/main.go.
 	}
diff --git a/internal/ior_mode_test.go b/internal/ior_mode_test.go
index 5ba2894..81fd314 100644
--- a/internal/ior_mode_test.go
+++ b/internal/ior_mode_test.go
@@ -31,12 +31,12 @@ import (
 // updating every test.
 func stubDeps() runnerDeps {
 	return runnerDeps{
-		getEUID:             func() int { return 0 },
-		runTrace:            func(flags.Config) error { return nil },
-		runParquet:          func(flags.Config) error { return nil },
-		runTraceWithContext: func(context.Context, flags.Config, chan<- struct{}, func(*eventLoop)) error { return nil },
-		runTUI:              func(flags.Config, runtime.TraceStarter) error { return nil },
-		runTUITestFlames:    func(flags.Config, runtime.TraceStarter) error { return nil },
+		getEUID:              func() int { return 0 },
+		runTrace:             func(flags.Config) error { return nil },
+		runParquet:           func(flags.Config) error { return nil },
+		runTraceWithContext:  func(context.Context, flags.Config, chan<- struct{}, func(*eventLoop)) error { return nil },
+		runTUI:               func(flags.Config, runtime.TraceStarter) error { return nil },
+		runTUITestFlames:     func(flags.Config, runtime.TraceStarter) error { return nil },
 		runTUITestLiveFlames: func(flags.Config, runtime.TraceStarter) error { return nil },
 	}
 }
diff --git a/internal/runtime/runtime.go b/internal/runtime/runtime.go
index 307c012..d6500d4 100644
--- a/internal/runtime/runtime.go
+++ b/internal/runtime/runtime.go
@@ -199,8 +199,8 @@ func TraceFiltersFromContext(ctx context.Context) (globalfilter.Filter, bool) {
 var (
 	// *flamegraph.LiveTrie must satisfy both the read-only and mutating sides of
 	// the trie contract as well as the combined LiveTrieSource interface.
-	_ Snapshotter   = (*flamegraph.LiveTrie)(nil)
-	_ Configurator  = (*flamegraph.LiveTrie)(nil)
+	_ Snapshotter    = (*flamegraph.LiveTrie)(nil)
+	_ Configurator   = (*flamegraph.LiveTrie)(nil)
 	_ LiveTrieSource = (*flamegraph.LiveTrie)(nil)
 
 	// *probemanager.Manager must satisfy the probe-control surface exposed to the TUI.
diff --git a/internal/statsengine/engine.go b/internal/statsengine/engine.go
index 78dbe65..02aee37 100644
--- a/internal/statsengine/engine.go
+++ b/internal/statsengine/engine.go
@@ -209,8 +209,8 @@ func (e *Engine) captureSnapshotInputs() snapshotInputs {
 // and returns their results bundled together.
 func buildSubSnapshots(in snapshotInputs, elapsed time.Duration) subSnapshots {
 	var (
-		ss  subSnapshots
-		wg  sync.WaitGroup
+		ss subSnapshots
+		wg sync.WaitGroup
 	)
 
 	wg.Add(5)
diff --git a/internal/tui/dashboard/model.go b/internal/tui/dashboard/model.go
index 8548481..2535a90 100644
--- a/internal/tui/dashboard/model.go
+++ b/internal/tui/dashboard/model.go
@@ -84,8 +84,8 @@ type Model struct {
 	// autoResetEvery; autoResetStatus uses this to render the live
 	// countdown ("12s/30s") in the chrome. Updated on every arm
 	// (SetAutoResetInterval, focus regain, tick re-arm).
-	autoResetArmedAt time.Time
-	keys         common.KeyMap
+	autoResetArmedAt         time.Time
+	keys                     common.KeyMap
 	globalFilter             globalfilter.Filter
 	filterStack              []string
 	recordingStatus          string
diff --git a/internal/tui/flamegraph/model.go b/internal/tui/flamegraph/model.go
index 73285f9..c188323 100644
--- a/internal/tui/flamegraph/model.go
+++ b/internal/tui/flamegraph/model.go
@@ -1051,7 +1051,6 @@ func (m Model) rootSnapshotPath() string {
 	return m.ZoomNavigator.rootSnapshotPath(m.snapshot, m.frames)
 }
 
-
 // frameIndexAt delegates to the FrameAnimator package-level helper to convert
 // terminal coordinates (x, y) to a frame index, accounting for UI chrome.
 func (m Model) frameIndexAt(x, y int) int {
@@ -1063,7 +1062,6 @@ func (m Model) frameCoordToTargetRow(dataRow, availableRows int) int {
 	return frameCoordToTargetRow(m.frames, dataRow, availableRows)
 }
 
-
 func (m Model) withZoomLineage(frames []tuiFrame) []tuiFrame {
 	return applyZoomLineage(frames, m.snapshot, m.zoomPath, m.width)
 }
diff --git a/internal/tui/flamegraph/renderer.go b/internal/tui/flamegraph/renderer.go
index 8f0d09b..24b99ed 100644
--- a/internal/tui/flamegraph/renderer.go
+++ b/internal/tui/flamegraph/renderer.go
@@ -209,12 +209,12 @@ func semanticFrameColor(name string) (color.Color, bool) {
 // renderViewParams bundles the pre-computed layout parameters used by
 // RenderTerminalView helpers to avoid threading many individual arguments.
 type renderViewParams struct {
-	rowOffset    int
-	maxRow       int
-	barHeight    int
+	rowOffset     int
+	maxRow        int
+	barHeight     int
 	availableRows int
 	visibleFrames int
-	truncated    bool
+	truncated     bool
 }
 
 // computeRenderParams derives the row-layout parameters for a given frame set