refactor(droid-control): read atoms as files, not listed skills

[factory-ain3sh]

Description

What

droid-control's ten atoms (terminal-use, true-input, browser-use, desktop-use, droid-cli, pty-capture, capture, compose, verify, showcase) are no longer skills. They move to skills/droid-control/atoms/<atom>/ATOM.md, and droid-control reads them by absolute path. A session with the plugin installed now lists one skill instead of eleven, which frees about 1,680 characters of the skill listing.

Why

The CLI caps the skill listing at 1.5% of the compaction limit: 21,000 characters at 350k, and 15,000 at the 250k default. A skill whose description doesn't fit is listed as a bare name, and droids rarely load a bare name. The atoms used about 1,680 characters, although each description said "not invoked directly" and only droid-control's routing loads them. In a factory-mono session that space came out of the user's own skills: 55 of them were listed without descriptions.

How

Skill discovery stops at a directory that has a SKILL.md, and the atom files are named ATOM.md, so no loader lists them. Ground rule 3 in droid-control/SKILL.md now says atoms are files:

• Read ${DROID_PLUGIN_ROOT}/skills/droid-control/atoms/<atom>/ATOM.md, and never use the Skill tool for one.
• Where an atom writes the plugin-root variable, substitute the root.

The plugin loader expands ${DROID_PLUGIN_ROOT} in skill bodies to the installed path. The atom paths therefore hold for ~/.factory or ~/.factory-dev, for user, project, or org scope, and for any cache version. The platforms/*.md docs were already loaded this way.

Adding disable-model-invocation: true would also hide the atoms. The Skill tool would then still load them only because SkillExecutor doesn't enforce that flag, while the flag's documented contract says it blocks the tool. That would break as soon as the flag is enforced.

Related Issue

No ticket. This came up while measuring skill-listing budget use for Factory-AI/factory-mono#24262.

Reviewer Guide

Diff shape: 16 renames that only drop frontmatter, routing wording in droid-control/SKILL.md and the three commands, and path updates in the docs.
Review depth: Standard. It changes how prompts route to atoms, and that routing was verified in live sessions.
Read order:

1. plugins/droid-control/skills/droid-control/SKILL.md: ground rule 3 and the new Atoms index.
2. plugins/droid-control/commands/*.md: "read listed atoms".
3. plugins/droid-control/ARCHITECTURE.md: the atoms section and platform paths.

Open for pushback: atoms/<atom>/ATOM.md keeps each atom's relative platforms/ links unchanged. A flat atoms/<atom>.md layout would be shorter, but those links would need rewriting.

Risk & Impact

• A droid that ignores ground rule 3 may call the Skill tool for an atom and get "not found". No model did in the runs below, even when an older droid-control in the same session still listed atom skills.
• Atom files are read raw, so the plugin-root variable inside them is not expanded. Ground rule 3 gives the substitution. The platforms/*.md files already worked this way.
• Anything that loaded an atom by skill name would break. user-invocable: false already hid the atoms from slash commands. Nothing in this repo, factory-mono, or ain3sh/.agents names them as skills.
• The change reverts as a single commit.

Verification

Behavior verified @ 07208ee: The plugin was installed through a local marketplace at project scope, into a cache path that contains spaces (~/.factory/plugins/cache/dc atoms mp-…/droid-control-…/e48ab4de515c/). Three models (Opus 5.5, GPT-6.1 Sol, GLM 5.3 Flash) were each asked to plan a single-clip htop demo through droid-control and stop before launching anything.

	master	This PR
Atoms loaded	terminal-use, capture, compose, verify (Sol through the Skill tool, Opus by reading the SKILL.md files)	The same four, read from atoms/<atom>/ATOM.md in the installed cache, on all three models
Skill tool calls for atoms	4 (Sol)	0
tctl	Resolved	Resolved and quoted under the spaced cache path
Skill listing with only this version active	droid-control and 10 atoms	droid-control only

Not tested: Recording and rendering, because tctl and render-showcase.sh are unchanged. Windows and macOS hosts.
Standard validators: droid-control tests pass (17 passed, 3 skipped). The check-skills workflow script passes locally, and every relative Markdown link under the plugin resolves.