spec: add gantt-dependencies specification (#3831)

## New Specification: `gantt-dependencies`

Related to #3830

---

### specification.md

# gantt-dependencies: Gantt Chart with Dependencies

## Description

A Gantt chart that visualizes project schedules with task dependencies
and groupings. Beyond displaying task timelines, this chart shows
relationships between tasks using connector arrows, indicating which
tasks must complete before others can begin. Tasks can be organized into
groups (phases or work packages) with aggregate timeline bars showing
the span of each group. This visualization is essential for
understanding critical paths and scheduling constraints in complex
projects.

## Applications

- Project management to visualize task sequences and identify critical
path dependencies
- Software development sprint planning showing feature dependencies and
blockers
- Construction project scheduling where certain phases must complete
before others begin
- Manufacturing workflow planning to coordinate sequential and parallel
operations

## Data

- `task` (str) - Name or description of the task
- `start` (datetime) - Start date/time of the task
- `end` (datetime) - End date/time of the task
- `group` (str, optional) - Parent group or phase for hierarchical
organization
- `depends_on` (list[str], optional) - List of task names that must
complete before this task starts
- Size: 10-50 tasks for optimal readability with dependencies
- Example: Software project with phases like "Requirements", "Design",
"Development", "Testing" where each phase contains multiple dependent
tasks

## Notes

- Draw dependency arrows/connectors from the end of predecessor tasks to
the start of successor tasks
- Use different visual styles for dependency types (finish-to-start is
most common)
- Group headers should show aggregate timeline spanning from earliest to
latest task in the group
- Consider indentation or color coding to distinguish groups from
individual tasks
- Arrows should avoid overlapping task bars where possible
- Include a legend explaining dependency line styles if multiple types
are used
- Vertical alignment should clearly show task hierarchy (groups above
their child tasks)

---

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---
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plots/gantt-dependencies/specification.md

@@ -0,0 +1,32 @@
+# gantt-dependencies: Gantt Chart with Dependencies
+
+## Description
+
+A Gantt chart that visualizes project schedules with task dependencies and groupings. Beyond displaying task timelines, this chart shows relationships between tasks using connector arrows, indicating which tasks must complete before others can begin. Tasks can be organized into groups (phases or work packages) with aggregate timeline bars showing the span of each group. This visualization is essential for understanding critical paths and scheduling constraints in complex projects.
+
+## Applications
+
+- Project management to visualize task sequences and identify critical path dependencies
+- Software development sprint planning showing feature dependencies and blockers
+- Construction project scheduling where certain phases must complete before others begin
+- Manufacturing workflow planning to coordinate sequential and parallel operations
+
+## Data
+
+- `task` (str) - Name or description of the task
+- `start` (datetime) - Start date/time of the task
+- `end` (datetime) - End date/time of the task
+- `group` (str, optional) - Parent group or phase for hierarchical organization
+- `depends_on` (list[str], optional) - List of task names that must complete before this task starts
+- Size: 10-50 tasks for optimal readability with dependencies
+- Example: Software project with phases like "Requirements", "Design", "Development", "Testing" where each phase contains multiple dependent tasks
+
+## Notes
+
+- Draw dependency arrows/connectors from the end of predecessor tasks to the start of successor tasks
+- Use different visual styles for dependency types (finish-to-start is most common)
+- Group headers should show aggregate timeline spanning from earliest to latest task in the group
+- Consider indentation or color coding to distinguish groups from individual tasks
+- Arrows should avoid overlapping task bars where possible
+- Include a legend explaining dependency line styles if multiple types are used
+- Vertical alignment should clearly show task hierarchy (groups above their child tasks)

plots/gantt-dependencies/specification.yaml

@@ -0,0 +1,29 @@
+# Specification-level metadata for gantt-dependencies
+# Auto-synced to PostgreSQL on push to main
+
+spec_id: gantt-dependencies
+title: Gantt Chart with Dependencies
+
+# Specification tracking
+created: 2026-01-15T20:43:22Z
+updated: 2026-01-15T20:43:22Z
+issue: 3830
+suggested: Eifi1
+
+# Classification tags (applies to all library implementations)
+# See docs/reference/tagging-system.md for detailed guidelines
+tags:
+  plot_type:
+    - gantt
+    - bar
+  data_type:
+    - datetime
+    - categorical
+    - relational
+  domain:
+    - business
+    - project-management
+  features:
+    - grouped
+    - hierarchical
+    - annotated