fix: use HTTP MCP server for Kiro 2.14.1+ so @agentbridge tools load

[Strobotti]

Summary

Fixes #948.

In Kiro CLI sessions, only `web_fetch`/`web_search` were available — none of the `@agentbridge/` MCP tools loaded, leaving the agent with effectively no IDE/file tools.

Root cause

Kiro 2.14.1 advertises `mcpCapabilities: { http: true, sse: false }` during ACP `initialize`, but `KiroClient.customizeNewSession()` injected a stdio MCP server via `buildMcpStdioServer()`. Kiro 2.14.1 silently ignores stdio MCP servers passed over ACP, so `_kiro.dev/mcp/server_initialized` never fired and no tools loaded.

Switching to an HTTP MCP server (pointing at the already-running `McpHttpServer`) surfaced a second, subtler bug: Kiro's `session/new` parser requires the HTTP server entry to carry a `headers` field as a JSON array (even empty `[]`). Without it — or with `headers` as an object — Kiro exits cleanly (exit code 0, no stderr, never connecting to MCP) the instant it parses `session/new`, killing the whole session.

The correct shape is:
```json
{"type":"http","name":"agentbridge","url":"http://127.0.0.1:/mcp","headers":[]}
```

The fix

• `AcpClient`: added `buildMcpHttpServer()` / `buildMcpHttpServerJson()` that emit the HTTP MCP server entry including the mandatory empty `headers` array, plus `advertisesHttpMcp()` to honor `mcpCapabilities.http`.
• `KiroClient.customizeNewSession()`: for Kiro ≥ 2.14.1 that advertises HTTP MCP, inject the HTTP server instead of stdio. Older versions fall back to stdio (no worse than before). The version gate is a conservative safeguard since older Kiro couldn't be re-verified.
• Added unit tests covering the HTTP MCP JSON shape (including the `headers:[]` array).

Verification

• A/B tested directly over ACP against real kiro-cli 2.14.1 (`--agent-engine v2`): stdio ❌, http+`headers:[]` ✅ — Kiro emits `_kiro.dev/mcp/server_initialized: agentbridge` and POSTs `initialize → notifications/initialized → tools/list`.
• Verified end-to-end in the real IntelliJ sandbox: all `@agentbridge/` tools now load in Kiro sessions.
• Unit tests pass.

[github-actions]

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[Strobotti]

here's a screenshot with the fix applied:

[catatafishen]

Thanks, I appreciate the help!

As a side note, I can no longer verify Kiro end to end. My account got banned for “suspicious activity,” and when I created a new one with another email, the same thing happened after a few days. I guess they’re quite sensitive to ACP-related testing, so it’s probably worth being careful when trying things out.