feat(t-paliad-177): ShapeTimeline enum + render_spec wiring

Slice 4 step 1 (faraday-Q7). RenderShape gets a fourth member
ShapeTimeline, AllShapes extends, Validate accepts it. The
companion TimelineConfig struct stores the saved palette / density /
range-preset for a CV-timeline view so re-opening the view restores
the same visual settings — same vocabulary as the standalone
/projects/{id}/chart URL state, just persisted in user_views.render_spec
instead of the URL.

Validator mirrors the frontend's enum guards:
- known palettes (default | kind-coded | track-coded | high-contrast | print)
- known densities (compact | standard | spacious)
- known range presets (1y | 2y | all | custom)
- ISO-date strings length-bounded to 32 chars so a hostile editor
  can't bloat the jsonb column.

Tests pin every accept/reject path in TestRenderSpec_TimelineConfigValidates.

Design ref: docs/design-project-chart-2026-05-09.md §11.5 + §14 Q7.

internal/services/render_spec.go

@@ -24,11 +24,19 @@ const (
 	ShapeList     RenderShape = "list"
 	ShapeCards    RenderShape = "cards"
 	ShapeCalendar RenderShape = "calendar"
+	// ShapeTimeline (t-paliad-177 Slice 4, faraday-Q7): cross-project
+	// horizontal chart rendered by frontend/src/client/views/shape-
+	// timeline-cv.ts on top of the same SVG renderer that powers
+	// /projects/{id}/chart. Lane axis = project_id. Adapter is lossy:
+	// ProjectionService projected rows are NOT surfaced (ViewService
+	// doesn't run the calculator). UI tooltip on first open documents
+	// the limitation.
+	ShapeTimeline RenderShape = "timeline"
 )
 
 // AllShapes lists every supported shape. Used by the validator and by
 // the in-page shape switcher.
-var AllShapes = []RenderShape{ShapeList, ShapeCards, ShapeCalendar}
+var AllShapes = []RenderShape{ShapeList, ShapeCards, ShapeCalendar, ShapeTimeline}
 
 // RenderSpec is the top-level render description.
 //
@@ -36,10 +44,25 @@ var AllShapes = []RenderShape{ShapeList, ShapeCards, ShapeCalendar}
 // is selected, so flipping back to a previously-used shape preserves
 // its tweaks (Q5 design decision).
 type RenderSpec struct {
-	Shape    RenderShape    `json:"shape"`
-	List     *ListConfig    `json:"list,omitempty"`
-	Cards    *CardsConfig   `json:"cards,omitempty"`
+	Shape    RenderShape     `json:"shape"`
+	List     *ListConfig     `json:"list,omitempty"`
+	Cards    *CardsConfig    `json:"cards,omitempty"`
 	Calendar *CalendarConfig `json:"calendar,omitempty"`
+	Timeline *TimelineConfig `json:"timeline,omitempty"`
+}
+
+// TimelineConfig is the per-shape config for shape=timeline. Mirrors the
+// URL-state knobs of the standalone /projects/{id}/chart page: a saved
+// CV-timeline view bakes the user's chosen palette / density / range
+// preset into render_spec so reopening the view restores the same
+// visual. None are required — empty defaults match the standalone
+// chart's defaults (default palette, standard density, 1y range).
+type TimelineConfig struct {
+	Palette     string `json:"palette,omitempty"`
+	Density     string `json:"density,omitempty"`
+	RangePreset string `json:"range_preset,omitempty"`
+	RangeFrom   string `json:"range_from,omitempty"`
+	RangeTo     string `json:"range_to,omitempty"`
 }
 
 // ListConfig is the per-shape config for shape=list. Powers both the
@@ -144,7 +167,7 @@ func (s *RenderSpec) Validate() error {
 		return fmt.Errorf("%w: render_spec is required", ErrInvalidInput)
 	}
 	switch s.Shape {
-	case ShapeList, ShapeCards, ShapeCalendar:
+	case ShapeList, ShapeCards, ShapeCalendar, ShapeTimeline:
 		// fine
 	default:
 		return fmt.Errorf("%w: unknown render_spec.shape %q", ErrInvalidInput, s.Shape)
@@ -165,6 +188,49 @@ func (s *RenderSpec) Validate() error {
 			return err
 		}
 	}
+	if s.Timeline != nil {
+		if err := s.Timeline.validate(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// KnownTimelinePalettes / Densities / Ranges mirror the frontend enums
+// in shape-timeline-chart.ts. Anything outside this set is rejected so
+// a stray value from an old build / hostile editor can't sneak into
+// stored render_spec rows.
+var (
+	knownTimelinePalettes = []string{
+		"default", "kind-coded", "track-coded", "high-contrast", "print",
+	}
+	knownTimelineDensities = []string{
+		"compact", "standard", "spacious",
+	}
+	knownTimelineRanges = []string{
+		"1y", "2y", "all", "custom",
+	}
+)
+
+func (c *TimelineConfig) validate() error {
+	if c.Palette != "" && !slices.Contains(knownTimelinePalettes, c.Palette) {
+		return fmt.Errorf("%w: unknown timeline.palette %q", ErrInvalidInput, c.Palette)
+	}
+	if c.Density != "" && !slices.Contains(knownTimelineDensities, c.Density) {
+		return fmt.Errorf("%w: unknown timeline.density %q", ErrInvalidInput, c.Density)
+	}
+	if c.RangePreset != "" && !slices.Contains(knownTimelineRanges, c.RangePreset) {
+		return fmt.Errorf("%w: unknown timeline.range_preset %q", ErrInvalidInput, c.RangePreset)
+	}
+	// RangeFrom / RangeTo are free-form ISO dates — the frontend regex-
+	// checks them; here we only verify they're plain ASCII length-bounded
+	// so a giant string can't bloat the jsonb column.
+	if len(c.RangeFrom) > 32 {
+		return fmt.Errorf("%w: timeline.range_from too long", ErrInvalidInput)
+	}
+	if len(c.RangeTo) > 32 {
+		return fmt.Errorf("%w: timeline.range_to too long", ErrInvalidInput)
+	}
 	return nil
 }
 

internal/services/render_spec_test.go

@@ -15,7 +15,7 @@ func TestRenderSpec_HappyPath(t *testing.T) {
 }
 
 func TestRenderSpec_ShapeMustBeKnown(t *testing.T) {
-	cases := []RenderShape{ShapeList, ShapeCards, ShapeCalendar}
+	cases := []RenderShape{ShapeList, ShapeCards, ShapeCalendar, ShapeTimeline}
 	for _, sh := range cases {
 		t.Run(string(sh), func(t *testing.T) {
 			s := RenderSpec{Shape: sh}
@@ -26,6 +26,36 @@ func TestRenderSpec_ShapeMustBeKnown(t *testing.T) {
 	}
 }
 
+func TestRenderSpec_TimelineConfigValidates(t *testing.T) {
+	cases := []struct {
+		name string
+		cfg  TimelineConfig
+		ok   bool
+	}{
+		{"empty defaults are fine", TimelineConfig{}, true},
+		{"known palette", TimelineConfig{Palette: "kind-coded"}, true},
+		{"known density", TimelineConfig{Density: "compact"}, true},
+		{"known range preset", TimelineConfig{RangePreset: "2y"}, true},
+		{"custom range with bounds", TimelineConfig{RangePreset: "custom", RangeFrom: "2026-01-01", RangeTo: "2026-12-31"}, true},
+		{"unknown palette rejects", TimelineConfig{Palette: "neon"}, false},
+		{"unknown density rejects", TimelineConfig{Density: "tiny"}, false},
+		{"unknown range rejects", TimelineConfig{RangePreset: "10y"}, false},
+		{"oversized range_from rejects", TimelineConfig{RangeFrom: string(make([]byte, 64))}, false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			s := RenderSpec{Shape: ShapeTimeline, Timeline: &tc.cfg}
+			err := s.Validate()
+			if tc.ok && err != nil {
+				t.Fatalf("expected ok, got error: %v", err)
+			}
+			if !tc.ok && !errors.Is(err, ErrInvalidInput) {
+				t.Fatalf("expected ErrInvalidInput, got %v", err)
+			}
+		})
+	}
+}
+
 func TestRenderSpec_UnknownShapeRejects(t *testing.T) {
 	s := RenderSpec{Shape: "kanban"}
 	if err := s.Validate(); !errors.Is(err, ErrInvalidInput) {