feat: add Cursor, Codex, and OpenCode harnesses — maximize every AI coding tool

- AGENTS.md: universal cross-tool file read by Claude Code, Cursor, Codex, and OpenCode
- .cursor/: 15 hook events via hooks.json, 16 hook scripts with DRY adapter pattern,
  29 rules (9 common + 20 language-specific) with Cursor YAML frontmatter
- .codex/: reference config.toml, Codex-specific AGENTS.md supplement,
  10 skills ported to .agents/skills/ with openai.yaml metadata
- .opencode/: 3 new tools (format-code, lint-check, git-summary), 3 new hooks
  (shell.env, experimental.session.compacting, permission.ask), expanded instructions,
  version bumped to 1.6.0
- README: fixed Cursor section, added Codex section, added cross-tool parity table
- install.sh: now copies hooks.json + hooks/ for --target cursor

.opencode/tools/format-code.ts

@@ -0,0 +1,66 @@
+/**
+ * ECC Custom Tool: Format Code
+ *
+ * Language-aware code formatter that auto-detects the project's formatter.
+ * Supports: Biome/Prettier (JS/TS), Black (Python), gofmt (Go), rustfmt (Rust)
+ */
+
+import { tool } from "@opencode-ai/plugin"
+import { z } from "zod"
+
+export default tool({
+  name: "format-code",
+  description: "Format a file using the project's configured formatter. Auto-detects Biome, Prettier, Black, gofmt, or rustfmt.",
+  parameters: z.object({
+    filePath: z.string().describe("Path to the file to format"),
+    formatter: z.string().optional().describe("Override formatter: biome, prettier, black, gofmt, rustfmt (default: auto-detect)"),
+  }),
+  execute: async ({ filePath, formatter }, { $ }) => {
+    const ext = filePath.split(".").pop()?.toLowerCase() || ""
+
+    // Auto-detect formatter based on file extension and config files
+    let detected = formatter
+    if (!detected) {
+      if (["ts", "tsx", "js", "jsx", "json", "css", "scss"].includes(ext)) {
+        // Check for Biome first, then Prettier
+        try {
+          await $`test -f biome.json || test -f biome.jsonc`
+          detected = "biome"
+        } catch {
+          detected = "prettier"
+        }
+      } else if (["py", "pyi"].includes(ext)) {
+        detected = "black"
+      } else if (ext === "go") {
+        detected = "gofmt"
+      } else if (ext === "rs") {
+        detected = "rustfmt"
+      }
+    }
+
+    if (!detected) {
+      return { formatted: false, message: `No formatter detected for .${ext} files` }
+    }
+
+    const commands: Record<string, string> = {
+      biome: `npx @biomejs/biome format --write ${filePath}`,
+      prettier: `npx prettier --write ${filePath}`,
+      black: `black ${filePath}`,
+      gofmt: `gofmt -w ${filePath}`,
+      rustfmt: `rustfmt ${filePath}`,
+    }
+
+    const cmd = commands[detected]
+    if (!cmd) {
+      return { formatted: false, message: `Unknown formatter: ${detected}` }
+    }
+
+    try {
+      const result = await $`${cmd}`.text()
+      return { formatted: true, formatter: detected, output: result }
+    } catch (error: unknown) {
+      const err = error as { stderr?: string }
+      return { formatted: false, formatter: detected, error: err.stderr || "Format failed" }
+    }
+  },
+})