diff --git a/README.md b/README.md
index 4896755..5a44e06 100644
--- a/README.md
+++ b/README.md
@@ -228,6 +228,7 @@ The canonical list lives in [`models.json`](./models.json) — the single source
 | `CLAUDE_ALLOWED_TOOLS` | `Bash,Read,...,Agent` | Comma-separated tools to pre-approve |
 | `CLAUDE_SKIP_PERMISSIONS` | `false` | Bypass all permission checks |
 | `CLAUDE_MCP_CONFIG` | *(unset)* | Path to an MCP server config JSON, passed to the spawned `claude` as `--mcp-config` (both the `-p` path and TUI `OCP_TUI_FULL_TOOLS` panes) |
+| `CLAUDE_SYSTEM_PROMPT` | *(unset)* | Operator-wide system-prompt text appended (last) to every request's composed system prompt on the default `-p` path. TUI-mode panes are unaffected (they keep the interactive CLI's own system prompt). Echoed truncated on `/health.systemPrompt`. Note: the response cache key does not include server config — after changing this value, flush the cache (`ocp clear`) or let TTL expire. |
 | `CLAUDE_NO_CONTEXT` | `false` | Suppress CLAUDE.md and auto-memory injection (pure API mode) |
 | `PROXY_API_KEY` | *(unset)* | Bearer token for shared-mode authentication |
 | `PROXY_ANONYMOUS_KEY` | *(unset)* | Well-known anonymous key (multi mode) — this exact string bypasses `validateKey()` and grants public access. Exposed via `/health.anonymousKey` only to localhost, or to all callers when `PROXY_ADVERTISE_ANON_KEY=1`. Full setup + security notes: [docs/lan-mode.md § Anonymous Access](docs/lan-mode.md#anonymous-access-optional). |
diff --git a/lib/prompt.mjs b/lib/prompt.mjs
new file mode 100644
index 0000000..2c38d56
--- /dev/null
+++ b/lib/prompt.mjs
@@ -0,0 +1,17 @@
+// lib/prompt.mjs — pure operator-append step for the system prompt.
+//
+// Extracted so the rule is unit-testable (the suite never imports server.mjs — it
+// boots a listener). server.mjs composes wrapper + client system messages exactly as
+// before, then passes the result through this. With CLAUDE_SYSTEM_PROMPT unset the
+// return is the INPUT STRING UNCHANGED — the default path stays byte-for-byte
+// identical, which is the repo's bar for touching a request-shaping function.
+//
+// The operator prompt goes LAST deliberately: a server-wide directive ("answer in
+// Chinese") should read as the final instruction, not something a client system
+// message overrides by coming later. Whitespace-only values are treated as unset —
+// a stray space in a service unit's Environment= line must not inject "\n\n " into
+// every request.
+export function appendOperatorPrompt(base, operatorAppend) {
+  const op = typeof operatorAppend === "string" ? operatorAppend.trim() : "";
+  return op ? `${base}\n\n${op}` : base;
+}
diff --git a/server.mjs b/server.mjs
index b908f49..d10c460 100644
--- a/server.mjs
+++ b/server.mjs
@@ -49,6 +49,7 @@ import { TuiSemaphore, SemaphoreAbortError, recordTuiEntrypoint, buildTuiHealthB
 import { TuiPanePool, resolvePoolSize, POOL_MAX_SIZE } from "./lib/tui/pool.mjs";
 import { TuiDeltaAssembler, DEFAULT_HOLDBACK_CHARS, resolveStreamHoldback } from "./lib/tui/stream.mjs";
 import { createSerialMutex, createTtlCache, isTokenExpiring, orderLabelsLastGoodFirst } from "./lib/spawn-auth.mjs";
+import { appendOperatorPrompt } from "./lib/prompt.mjs";
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
 const _pkg = JSON.parse(readFileSync(join(__dirname, "package.json"), "utf8"));
@@ -195,17 +196,19 @@ function resolveClaude() {
 const OCP_SYSTEM_PROMPT_WRAPPER = `You are accessed via the OCP HTTP proxy. You do NOT have access to any local filesystem, working directory, shell, git status, or machine environment. Do not infer or invent such information from any context you observe. Respond only based on the conversation provided.`;
 
 // Build the full system-prompt string: OCP_SYSTEM_PROMPT_WRAPPER prepended,
-// then any system-role messages from the request appended (separated by blank line).
-// ADR 0009 Amendment 1 analogue § "OLP system prompt wrapper".
+// then any system-role messages from the request appended (separated by blank line),
+// then the operator-wide CLAUDE_SYSTEM_PROMPT appended LAST (lib/prompt.mjs — a
+// no-op returning the same string when the var is unset, so the default path is
+// byte-for-byte unchanged). ADR 0009 Amendment 1 analogue § "OLP system prompt wrapper".
 function extractSystemPrompt(messages) {
   const systemMessages = (messages ?? []).filter(m => m.role === "system");
   if (systemMessages.length === 0) {
-    return OCP_SYSTEM_PROMPT_WRAPPER;
+    return appendOperatorPrompt(OCP_SYSTEM_PROMPT_WRAPPER, SYSTEM_PROMPT);
   }
   const clientContent = systemMessages.map(m =>
     contentToText(m.content)
   ).join("\n\n");
-  return `${OCP_SYSTEM_PROMPT_WRAPPER}\n\n${clientContent}`;
+  return appendOperatorPrompt(`${OCP_SYSTEM_PROMPT_WRAPPER}\n\n${clientContent}`, SYSTEM_PROMPT);
 }
 
 // ── NDJSON line buffer parser (Phase 6c port) ─────────────────────────────
diff --git a/test-features.mjs b/test-features.mjs
index 04fd6d8..2af7ef8 100644
--- a/test-features.mjs
+++ b/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";