fix(opencode): add resolvable package entry and loadable in-place sources

Root package.json declared no main or exports, so OpenCode npm plugin
resolution (import.meta.resolve) failed and the plugin was silently
skipped (#3127). The .opencode TypeScript sources imported siblings
with .js specifiers that only exist after compilation, so the home
install, which loads the .ts files in place, crashed the tool registry
with ERR_MODULE_NOT_FOUND (#3112).

Declare main/types/exports on the root package pointing at the
compiled plugin entry, switch the sources to .ts specifiers, and
enable allowImportingTsExtensions with rewriteRelativeImportExtensions
so the emitted dist keeps working .js specifiers. Add smoke tests that
build the package, resolve and import the entry by name from a temp
install, and verify every in-place relative import resolves.

Fixes #3127
Fixes #3112

tests/scripts/build-opencode.test.js

@@ -4,6 +4,7 @@
 
 const assert = require("assert")
 const fs = require("fs")
+const os = require("os")
 const path = require("path")
 const { spawnSync } = require("child_process")
 const { getNpmPackEntry } = require("../lib/npm-pack-output")
@@ -46,6 +47,72 @@ function main() {
       assert.strictEqual(result.status, 0, result.stderr)
       assert.ok(fs.existsSync(distEntry), ".opencode/dist/index.js should exist after build")
     }],
+    ["package.json declares a resolvable OpenCode plugin entry", () => {
+      assert.strictEqual(packageJson.main, ".opencode/dist/index.js")
+      assert.ok(packageJson.exports, "package.json must declare an exports map")
+      assert.deepStrictEqual(packageJson.exports["."], {
+        types: "./.opencode/dist/index.d.ts",
+        import: "./.opencode/dist/index.js",
+        default: "./.opencode/dist/index.js",
+      })
+    }],
+    ["installed package resolves and imports its root module by name", () => {
+      const tempDir = fs.mkdtempSync(path.join(os.tmpdir(), "ecc-opencode-entry-"))
+      try {
+        fs.mkdirSync(path.join(tempDir, "node_modules"), { recursive: true })
+        fs.symlinkSync(
+          repoRoot,
+          path.join(tempDir, "node_modules", "ecc-universal"),
+          process.platform === "win32" ? "junction" : "dir"
+        )
+        const probe = `
+          const resolved = import.meta.resolve("ecc-universal")
+          if (!resolved.endsWith("/.opencode/dist/index.js")) {
+            throw new Error("unexpected entry resolution: " + resolved)
+          }
+          const mod = await import("ecc-universal")
+          if (Object.keys(mod).join(",") !== "default" || typeof mod.default !== "function") {
+            throw new Error("root module must export exactly the plugin function")
+          }
+        `
+        const probePath = path.join(tempDir, "probe.mjs")
+        fs.writeFileSync(probePath, probe)
+        const result = spawnSync(process.execPath, [probePath], {
+          cwd: tempDir,
+          encoding: "utf8",
+        })
+        assert.strictEqual(result.status, 0, result.stderr)
+      } finally {
+        fs.rmSync(tempDir, { recursive: true, force: true })
+      }
+    }],
+    ["OpenCode TypeScript sources resolve their relative imports in place", () => {
+      const opencodeDir = path.join(repoRoot, ".opencode")
+      const sourceFiles = []
+      const walk = (dir) => {
+        for (const entry of fs.readdirSync(dir, { withFileTypes: true })) {
+          const entryPath = path.join(dir, entry.name)
+          if (entry.isDirectory()) {
+            if (entry.name !== "node_modules" && entry.name !== "dist") walk(entryPath)
+          } else if (entry.name.endsWith(".ts")) {
+            sourceFiles.push(entryPath)
+          }
+        }
+      }
+      walk(opencodeDir)
+      assert.ok(sourceFiles.length > 0, "expected OpenCode TypeScript sources")
+      const unresolved = []
+      for (const sourceFile of sourceFiles) {
+        const source = fs.readFileSync(sourceFile, "utf8")
+        for (const match of source.matchAll(/(?:from|import)\s*\(?\s*"(\.[^"]+)"/g)) {
+          const target = path.resolve(path.dirname(sourceFile), match[1])
+          if (!fs.existsSync(target)) {
+            unresolved.push(`${path.relative(repoRoot, sourceFile)} -> ${match[1]}`)
+          }
+        }
+      }
+      assert.deepStrictEqual(unresolved, [])
+    }],
     ["built OpenCode entry exports only the plugin function", () => {
       const check = `
         const assert = require("assert")