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/session/engine.ts

@@ -353,6 +353,7 @@ export class Engine {
     if (!t?.requires) return true
     if (t.requires === "vision") return this.model.spec.vision === true
     if (t.requires === "project") return this.o.toolCtx.projectDir !== undefined
+    if (t.requires === "display") return this.o.toolCtx.show !== undefined
     if (t.requires === "knowledge") {
       const L = this.o.toolCtx.library
       const have = L?.lib.bases().filter((b) => b.documents > 0).map((b) => b.name) ?? []