Harness spec 3.1.0: the prefix stays still, in the CLI

The system prompt is made once per session (start, compaction, model
switch), kept in session_meta and resent byte for byte; it holds no
date. What changes mid-session -- the date, a mode the person chose, a
plan or memory or instruction file they edited, a personality, MCP
instructions that arrived later -- is a <session-note> on the next user
message, stored with it. The tool list is fixed for the session:
plan_submit is always offered and answers unavailable outside plan
mode, the wrap-up keeps the tools and runs no call, a withdrawn tool
stays listed and answers its refusal; the first request waits up to
mcp_wait_ms for MCP servers. Compaction asks for its summary as the
next turn of the same conversation. Cached input tokens are parsed
(incl. llama.cpp timings), stored per request and shown in /context.

Spec: context.md §7/§10, loop.json context.note (+ plan_ended,
plan_own, personal, empty, mcp_wait_ms), modes.json plan.refused,
compact.md without the transcript heading. Conformance area prefix.

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

tests/context.test.ts

@@ -66,7 +66,15 @@ describe("context", () => {
     a.bus.on((e: Event) => e.type === "notice" && notices.push(e.message))
     await a.engine.prompt("go")
     expect(notices.some((n) => n.includes("compacting the conversation"))).toBe(true)
-    expect(fake!.requests[1].messages[0].content).toContain("## Transcript")
+    // The summary is the next turn of the same conversation (context.md §7, spec 3.1.0): the same
+    // system prompt and tools, every message as it was, then the compaction text — no transcript.
+    const [first, compaction] = [fake!.requests[0], fake!.requests[1]]
+    expect(compaction.messages[0]).toEqual(first.messages[0])
+    expect(compaction.tools).toEqual(first.tools)
+    expect(compaction.messages.slice(0, first.messages.length)).toEqual(first.messages)
+    expect(compaction.messages.at(-2).role).toBe("tool")
+    expect(compaction.messages.at(-1).content).toStartWith("Summarise the conversation")
+    expect(compaction.messages.at(-1).content).not.toContain("yyyy")
     const last = fake!.requests[2].messages
     expect(JSON.stringify(last[1])).toContain("A long task.")
     // the original request comes back verbatim, with the note
@@ -77,7 +85,7 @@ describe("context", () => {
   test("/context: parts of the system prompt, tools, the conversation, against the window", async () => {
     const a = app(`connections:\n  f:\n    type: webui\n    url: URL\n    models: { f/m: { context: 32768 } }\n`, [{ chunks: [toolCall(0, "c1", "read", '{"path":"big.txt"}'), usage(1500, 20)] }, { chunks: [delta({ content: "ok" }), usage(3100, 5)] }])
     await a.engine.prompt("read it")
-    const system = a.engine.o.system(a.engine.mode, a.engine.model)
+    const system = a.engine.compose(a.engine.mode)
     const text = renderBreakdown(contextBreakdown(a.engine, system, [], undefined, a.engine.o.tools))
     expect(text).toContain("window 32.8k")
     expect(text).toContain("system prompt")