A guide for adding a draggable divider to a two-pane plugin layout, such as a sidebar beside main content. It explains how to handle mouse dragging, limit pane widths, save the chosen size, and manage the layout.

Use it when building resizable sidebars, drag interactions, or layouts where users adjust the width of two panes.

It removes the need to design the resizing interaction and its state handling from scratch. It also shows how similar plugins already implement the pattern.

drag-pane — Skill for Claude Code by marcus/sidecar

About the project

Sidecar is a terminal-based workspace for running AI coding agents alongside file trees, task issues, Git diffs, and Jira or GitHub resources in split panes. Developers use it to monitor agent sessions, inspect files and changes, manage workspaces, and handle tasks without leaving one shell. The catalogue entries extend or guide coding-agent workflows used with Sidecar.

marcus/sidecar · 1,091 stars · on GitHub

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent

npx skills add marcus/sidecar --skill drag-pane

Clone the repo

git clone --depth 1 https://github.com/marcus/sidecar

Made for: Claude Code.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/skills/marcus/sidecar/drag-pane/github.svg)](https://agentmods.dev/skills/marcus/sidecar/drag-pane)

Your own site

<a href="https://agentmods.dev/skills/marcus/sidecar/drag-pane"><img src="https://agentmods.dev/badge/skills/marcus/sidecar/drag-pane/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/skills/marcus/sidecar/drag-pane"><img src="https://agentmods.dev/badge/skills/marcus/sidecar/drag-pane.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 70 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.

When invoked 3,795 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits

NVIDIA SkillSpector pass 7 Sept 2026

How audits are shown

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.00070	$0.03795
Opus 5.5	$0.00028	$0.01518
Sonnet 5.5	$0.00014	$0.00759
Haiku 4.5	$0.00007	$0.00380

Measured 1mo ago against content hash 91beda9d2b60, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

drag-pane scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 1mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/drag-pane/SKILL.md · 422 lines

How it starts

The opening of the file, as written. The whole thing — 422 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Drag-to-Resize Pane Implementation

Overview

Add drag-to-resize support for two-pane plugin layouts (sidebar + main content). Users click and drag the divider between panes to resize them.

Prerequisites

Plugin already has a two-pane layout (sidebar + main content)
State persistence functions exist in internal/state/state.go (each plugin has its own getter/setter)
Familiarity with internal/mouse package

Existing Implementations

Plugin	State Functions	Mouse File
FileBrowser	`GetFileBrowserTreeWidth()` / `SetFileBrowserTreeWidth()`	`internal/plugins/filebrowser/mouse.go`
GitStatus	`GetGitStatusSidebarWidth()` / `SetGitStatusSidebarWidth()`	`internal/plugins/gitstatus/mouse.go`
Conversations	`GetConversationsSideWidth()` / `SetConversationsSideWidth()`	`internal/plugins/conversations/mouse.go`
Workspace (project)	`GetWorkspaceSidebarWidth()` / `SetWorkspaceSidebarWidth()`	`internal/plugins/workspace/view_list.go`
Sessions (global workspace)	`GetWorkspaceSidebarWidth()` / `SetWorkspaceSidebarWidth()`	`internal/overview/workspaces.go`

Windowing parity: project and global workspaces are one feature

The project workspace (internal/plugins/workspace) and the global Workspaces browser shown as Sessions in the navbar (internal/overview) are two projections of the same windowing model. They are not independent surfaces that happen to look similar.

If a change affects panes, splits, drag handles, pane borders, focus chrome, or pane hit regions in one of them, it affects the other. The rule is structural, not a habit to remember:

internal/panelayout owns pane-tree structure and geometry.
internal/paneframe owns presentation: chrome geometry (Inset, Geometry), the leaf border states (Chrome, WrapLeaf), the drag handle (RenderDividerHandle, DividerHitBox, HandleStateFor), the compositor (Compose, ComposeLeaf, RenderContent), the chrome-aware floors (ChromeFloors), and the one order hit regions are registered in (RegisterRegions), and click-to-focus (LeafAt, FocusLeafAt).
Each surface implements paneframe.Host and paneframe.RegionSink in exactly one file: internal/plugins/workspace/pane_host.go and internal/overview/pane_host.go.

Read the full file on GitHub · 422 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

1mo ago Changed · +38 lines 91beda9d2b60
1mo ago First seen · 384 lines · 70 tokens per session scan A aad5a0eab995

Subscribe to this mod's changes

drag-pane is a skill published in the GitHub repository marcus/sidecar (1,091 stars, last pushed 11d ago), licensed MIT. It adds 70 tokens to every session and 3,795 once invoked, about $0.0003 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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drag-pane