CLI loads harness spec 3.0.0-draft; the show tool over the link

The spec's version may be a pre-release (3.0.0-draft). Every tool file is
loaded, with the new fields `sessions`, `requires`, `unavailable` and
`confirm`; the CLI's tools are those not the server's alone and offered in an
agent session (forCli) — a chat's own tools over the server's tree (mkdir, mv,
rm, search, python, the forge verbs) are not built in. blocks/context.md is
known; blocks/workspace.md is the server's alone.

show is built in with `requires: display`: offered only in a session a client
opened over the link when that client said `show: true` (capability `show`);
the device reads the file (at most 1 MB) and sends it with `_lembas/show`.
The harness tests now say 3.0.0's split of tools instead of "the execution
tools are the CLI's alone".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/tool/show.ts

@@ -0,0 +1,76 @@
+// show (harness spec 3.0.0): a file opened in the user's viewer beside the conversation. A terminal
+// has no such viewer, so the tool is offered only in a session a client opened over the link and
+// only when that client said it can show files (`show: true`, harness/acp.md `_lembas/show`): the
+// device reads the file and sends it, since the client cannot reach this disk.
+import { statSync } from "node:fs"
+import { basename, extname, relative } from "node:path"
+import { z } from "zod"
+import { described, TOOL_SPECS } from "../harness.ts"
+import { absPath, defineTool, readText, showPath, ToolError } from "./tool.ts"
+
+/** The most a file may be to be sent (acp.md: at most 1 MB; a larger one is refused before sending). */
+export const SHOW_MAX_BYTES = 1024 * 1024
+
+/** The answer when nothing can be shown (spec `unavailable`), word for word. */
+export const SHOW_UNAVAILABLE = TOOL_SPECS.show!.unavailable!
+
+/** What `_lembas/show` carries for one file. */
+export interface ShowRequest {
+  path: string
+  kind: "markdown" | "code" | "text" | "html"
+  language?: string
+  line?: number
+  text: string
+}
+
+export type ShowReply = { shown: true } | { shown: false; reason: string }
+
+// A known source extension is code, with its language; the list is the viewer's highlighters.
+const LANGUAGES: Record<string, string> = {
+  ts: "typescript", tsx: "tsx", js: "javascript", mjs: "javascript", cjs: "javascript", jsx: "jsx", json: "json", py: "python", rs: "rust", go: "go",
+  rb: "ruby", php: "php", java: "java", kt: "kotlin", swift: "swift", c: "c", h: "c", cc: "cpp", cpp: "cpp", hpp: "cpp", cs: "csharp",
+  sh: "bash", bash: "bash", zsh: "bash", fish: "fish", css: "css", scss: "scss", sql: "sql", yaml: "yaml", yml: "yaml", toml: "toml",
+  xml: "xml", svg: "xml", lua: "lua", zig: "zig", dart: "dart", vue: "vue", svelte: "svelte",
+}
+
+/** The viewer's kind for a file, by its name (acp.md): `.md` markdown, `.html`/`.htm` html, a known
+ *  source extension code, anything else text. */
+export function showKind(path: string): { kind: ShowRequest["kind"]; language?: string } {
+  const ext = extname(path).slice(1).toLowerCase()
+  if (ext === "md" || ext === "markdown") return { kind: "markdown" }
+  if (ext === "html" || ext === "htm") return { kind: "html" }
+  const language = LANGUAGES[ext] ?? (basename(path) === "Dockerfile" ? "dockerfile" : basename(path) === "Makefile" ? "makefile" : undefined)
+  return language ? { kind: "code", language } : { kind: "text" }
+}
+
+export const showTool = defineTool({
+  ...described("show"),
+  access: "show",
+  requires: "display",
+  schema: z.object({ path: z.string(), line: z.number().int().min(1).optional() }),
+  permission: (a, ctx) => {
+    const abs = absPath(a.path, ctx)
+    return { permission: "show", class: "interact", patterns: [showPath(abs, ctx)], paths: [abs] }
+  },
+  async run(a, ctx) {
+    // Offered with a display; one that went away since answers the spec's sentence.
+    if (!ctx.show) return { output: SHOW_UNAVAILABLE, isError: true }
+    const abs = absPath(a.path, ctx)
+    let size: number
+    try {
+      const st = statSync(abs)
+      if (!st.isFile()) throw new ToolError(`${showPath(abs, ctx)} is not a file.`)
+      size = st.size
+    } catch (e) {
+      if (e instanceof ToolError) throw e
+      throw new ToolError(`${showPath(abs, ctx)} does not exist. Write it first.`)
+    }
+    if (size > SHOW_MAX_BYTES) throw new ToolError(`${showPath(abs, ctx)} is ${Math.round(size / 1024)} KB; at most 1 MB can be shown. Give the user the path instead.`)
+    const text = await readText(abs)
+    if (text.includes("\u0000")) throw new ToolError(`${showPath(abs, ctx)} is not a text file; it cannot be shown. Give the user the path instead.`)
+    const rel = relative(ctx.cwd, abs) || basename(abs)
+    const reply = await ctx.show({ path: rel, ...showKind(abs), ...(a.line ? { line: a.line } : {}), text }, ctx.callId)
+    if (!reply.shown) return { output: `Not shown: ${reply.reason}`, isError: true }
+    return { output: `Shown to the user: ${showPath(abs, ctx)}${a.line ? ` at line ${a.line}` : ""}.`, title: showPath(abs, ctx) }
+  },
+})