Harness spec 1.1.0: one plan, prototypes and the library shared; the CLI implements it

The spec: plan_write and plan_update (new, shared, offered in every mode) and
plan_submit (now shared) keep one structured plan — findings, objectives,
phases of tasks — in place of the todo list, which lives on as a former name
of plan_write. The shared system text is one text for both projects, with
variables for what differs; the mode texts, a prototypes block and a library
block are shared. acp.md: the client hands the device what only it knows
(context, library, prototypes), the plan travels as a structure (plan_state),
library calls carry the chat's scope, and a client may rewind a session.
loop.json says its numbers as numbers. Four conformance areas: plan,
prototype, library_scope, toolcall_index.

The CLI: the plan is kept per session in the store and drawn above the prompt
and on the approval card; the prompt is assembled from the spec's texts with
their variables filled; the link reads the instance's instructions,
personalization, knowledge scope and prototype offer, sends the plan as a
structure and answers rewind; library calls to the instance carry the session
as scope; a prototype written in the terminal is saved as a file and named in
the transcript; a tool-call fragment without an index continues the last call;
the default theme is Moria; dead exports and Hermes leftovers removed.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/fill.test.ts

@@ -0,0 +1,16 @@
+// A prompt text's variables (harness spec, prompts/index.json): filled in, a bullet-only line
+// taken out with its empty variable, and a variable with no value refused rather than sent.
+import { expect, test } from "bun:test"
+import { fillPrompt } from "../src/prompt/fill.ts"
+
+test("a variable is filled; a line that is only a bullet and an empty variable disappears", () => {
+  const text = "{{intro}}\n\n# Using tools\n- {{surface}} Be concise.\n- {{tool_list}}\n  - {{file_tools}}\n- Keep working.\n* {{background}}\n\n{{git}}"
+  const out = fillPrompt(text, { intro: "You help.", surface: "A terminal.", tool_list: "", file_tools: "Use read.", background: "   ", git: "" })
+  expect(out).toBe("You help.\n\n# Using tools\n- A terminal. Be concise.\n  - Use read.\n- Keep working.\n\n")
+})
+
+test("a variable with no value is an error, not a literal {{name}} sent to the model", () => {
+  expect(() => fillPrompt("- {{plan_context}}\n{{intro}}", { intro: "x" })).toThrow("no value for {{plan_context}}")
+  // A filled variable may itself contain a bullet-and-variable line: it is text, not a template.
+  expect(fillPrompt("- {{a}}", { a: "- {{b}}" })).toBe("- - {{b}}")
+})