Add ECA (Editor Code Assistant) harness support

[lockie]

What problem are you trying to solve?

ECA (Editor Code Assistant) is an open-source AI pair programming tool (https://eca.dev) with a plugin system that supports skills, hooks, MCP servers, and agents. Users running ECA had no way to use Superpowers — the plugin system is compatible, but Superpowers lacked the .eca-plugin/ directory structure and hook definitions that ECA needs to discover and load the plugin.

What does this PR change?

Adds ECA as a supported harness by introducing a .eca-plugin/ directory with marketplace metadata, a chatStart hook that injects the using-superpowers bootstrap skill content at session start, and symlinks to the existing skills directory. Also adds an ECA tool-mapping reference and install documentation.

Is this change appropriate for the core library?

Yes. ECA is a general-purpose coding agent, not a project-specific or domain-specific tool. This adds a new harness integration using the same pattern as existing harnesses (Claude Code, Codex, Cursor, etc.). Skills, bootstrap injection, and tool mapping are general-purpose — they benefit anyone using ECA regardless of project type.

What alternatives did you consider?

• Submitting to the eca-plugins marketplace repo only: The official eca-plugins repo already has a lobotomized plugins/superpowers entry with skills only (no hooks). Adding hooks there would be a separate process and wouldn't give users the full Superpowers experience (no bootstrap injection). Hosting the plugin from the Superpowers repo itself gives users the complete integration.
• Requiring manual config in user's config.json hooks section: Could work but would require every user to manually configure the hook, which is error-prone and doesn't match the install experience of other harnesses.

Does this PR contain multiple unrelated changes?

No. All changes are part of a single new-harness integration.

Existing PRs

• I have reviewed all open AND closed PRs for duplicates or prior art
• Related PRs: none found

Environment tested

Harness	Harness version	Model	Model version/ID
ECA	0.138.1	GLM-5.1 (Coding Plan)	zai-coding-plan/glm-5.1

New harness support (required if this PR adds a new harness)

Clean-session transcript for "Let's make a react todo list"

Let's make a react todo list

I'll help you create a React todo list! Since this is a creative development task, I need to use the appropriate skills to guide our approach.
Loading skill 'superpowers:brainstorming' ✅ 0s


I'm using the brainstorming skill to help design your React todo list properly before we start building.
Listing tree: test ✅ 0s


Great! I can see this is a fresh project. Let me ask you some questions to understand what you're building.

**First question:** What's the primary purpose of this todo list? Is it:

A) A learning/experimental project to understand React basics
B) A fully functional personal todo app you plan to actually use
C) A portfolio/demo project to show others
D) Something else?

Evaluation

• Initial prompt: "Add ECA harness support to superpowers"
• Eval sessions: 2 (initial plugin setup + debugging hooks.json format, then clean verification session)
• Outcomes: brainstorming skill auto-triggers correctly at session start via chatStart hook

Rigor

• If this is a skills change: I used superpowers:writing-skills and completed adversarial pressure testing (paste results below)
• This change was tested adversarially, not just on the happy path
• I did not modify carefully-tuned content (Red Flags table, rationalizations, "human partner" language) without extensive evals showing the change is an improvement

No skills content was modified. Only infrastructure files were added/changed: plugin directory structure, hook definitions, tool mapping reference, and documentation.

Human review

• A human has reviewed the COMPLETE proposed diff before submission

Authoring environment disclosure

• Model: GLM-5.1 (Coding Plan) via zai-coding-plan
• Harness: ECA 0.138.1
• Harness version: 0.138.1
• Installed plugins: context-mode

🤖 Generated with ECA (zai-coding-plan/glm-5.1)

Co-Authored-By: eca-agent git@eca.dev