Add terminal and _meta capability support to initialize request

[timvisher-dd]

Fixes xenodium/agent-shell#342

See that issue for the full problem description and perf measurements.

Checklist

• I agree to communicate (PR description and comments) with the author myself (not AI-generated).
• I've reviewed all code in PR myself and will vouch for its quality.
• I've added tests where applicable.

Implementation

acp-make-initialize-request gains two new optional keyword arguments:

• :terminal-capability — boolean (or :false) controlling whether terminal appears in clientCapabilities. When nil (the default) it is omitted entirely, preserving backward compatibility.

• :meta-capabilities — an alist sent under the _meta key in clientCapabilities. This is where clients advertise support for extensions like terminal_output. When nil, _meta is omitted.

The existing :read-text-file-capability and :write-text-file-capability arguments are unchanged.

Example

(acp-make-initialize-request
 :protocol-version 1
 :client-info '((name . "agent-shell") (version . "1.0"))
 :read-text-file-capability t
 :write-text-file-capability t
 :terminal-capability t
 :meta-capabilities '((terminal_output . t)))

Produces JSON with:

{
  "clientCapabilities": {
    "fs": { "readTextFile": true, "writeTextFile": true },
    "terminal": true,
    "_meta": { "terminal_output": true }
  }
}

Tests

4 new tests in tests/acp-test.el:

• test-acp-make-initialize-request-omits-terminal-and-meta-when-nil — verifies backward compat: no terminal or _meta keys when args are nil.
• test-acp-make-initialize-request-terminal-true — terminal: true when :terminal-capability t.
• test-acp-make-initialize-request-terminal-false — terminal: false when :terminal-capability :false.
• test-acp-make-initialize-request-meta-capabilities — arbitrary alist is passed through under _meta.

[timvisher-dd]

This has been thoroughly battle tested at this point. Whether agent-shell chooses to land proper support for terminal and meta caps I see no reason why acp.el shouldn't allow clients to declare it. WDYT? :)

[timvisher-dd]

Closed by timvisher-dd#1