fix(server): wire CLAUDE_SYSTEM_PROMPT (dead since APPEND_SYSTEM_PROMPT retirement) (#175)

* fix(server): wire CLAUDE_SYSTEM_PROMPT into the composed system prompt (was dead since APPEND_SYSTEM_PROMPT retirement)

The var was read (SYSTEM_PROMPT, server.mjs), documented in the file header as
"appended to all requests", and echoed on /health.systemPrompt — but nothing on
the request path consumed it: extractSystemPrompt() composed only the wrapper +
client system messages. The wiring was lost when APPEND_SYSTEM_PROMPT was
retired, leaving the header comment and the buildCliArgs comment describing
behavior that did not exist (caught by the PR #170 independent reviewer).

Wire, not delete, because:
- the /health `systemPrompt` field is part of the grandfathered B.2 contract
  (ADR 0006, frozen at v3.16.4) — removal would need an ADR; wiring keeps the
  shape and makes the field honest;
- fleet check: no deployment sets the var (Mac prod plist, Oracle systemd unit,
  PI231 /etc/ocp/ocp.env all clean), so wiring changes behavior for NOBODY today;
- with the var unset, appendOperatorPrompt returns its input string unchanged —
  the default path is byte-for-byte identical.

Mechanics: new pure lib/prompt.mjs `appendOperatorPrompt(base, operatorAppend)`
(trimmed; whitespace-only treated as unset so a stray space in a service unit
cannot inject "\n\n " into every request), applied as the LAST segment in both
extractSystemPrompt branches — an operator-wide directive reads as the final
instruction, after client system messages. TUI-mode is untouched (panes keep the
interactive CLI's own system prompt); documented in the README row.

ALIGNMENT.md Rule 2: no cli.js citation applies. No endpoint, header, or wire
field is added or altered; the change affects only the CONTENT OCP passes to the
already-established `--system-prompt` flag (file header § verified v2.1.104),
i.e. OCP-owned prompt composition. /health shape unchanged.

Tests: +3, doubly mutation-proven (unconditional-base revert → 2 failures;
trim removal → 2 failures). Suite 341 passed / 0 failed.

Co-Authored-By: Claude <claude-opus-4-8> <noreply@anthropic.com>

* docs(readme): cache-staleness caveat on CLAUDE_SYSTEM_PROMPT row (reviewer advisory)

---------

Co-authored-by: dtzp555 <dtzp555@gmail.com>
Co-authored-by: Claude <claude-opus-4-8> <noreply@anthropic.com>

test-features.mjs

@@ -821,6 +821,32 @@ test("doctor falls back to currentVersion when origin/main unreachable (no stale
   assert.equal(result.next_action.kind, "noop");
 });
 
+// ── System-prompt operator append (CLAUDE_SYSTEM_PROMPT wiring) ─────────────
+// The var was documented + echoed on /health but never reached a request (dead
+// since APPEND_SYSTEM_PROMPT was retired — caught in PR #170 review). The wiring
+// contract lives in lib/prompt.mjs. Mutation-proof: make appendOperatorPrompt
+// return `base` unconditionally and the first test fails; make it stop trimming
+// and the whitespace test fails.
+import { appendOperatorPrompt } from "./lib/prompt.mjs";
+
+console.log("\nSystem-prompt operator append:");
+
+test("appendOperatorPrompt: appends the operator prompt LAST, blank-line separated", () => {
+  assert.equal(appendOperatorPrompt("WRAPPER\n\nclient", "Answer in Chinese."), "WRAPPER\n\nclient\n\nAnswer in Chinese.");
+});
+
+test("appendOperatorPrompt: unset/empty/whitespace-only → base returned BYTE-IDENTICAL", () => {
+  const base = "WRAPPER\n\nclient sys";
+  assert.equal(appendOperatorPrompt(base, undefined), base);
+  assert.equal(appendOperatorPrompt(base, ""), base);
+  assert.equal(appendOperatorPrompt(base, "   \n "), base, "a stray space in a service unit must not inject anything");
+  assert.equal(appendOperatorPrompt(base, null), base);
+});
+
+test("appendOperatorPrompt: operator value is trimmed before appending", () => {
+  assert.equal(appendOperatorPrompt("W", "  hi  "), "W\n\nhi");
+});
+
 // ── Upgrade Tests ──
 import { runUpgrade, postFlightOk } from "./scripts/upgrade.mjs";