diff --git a/src/agents/pi-embedded-runner/run/llm-idle-timeout.test.ts b/src/agents/pi-embedded-runner/run/llm-idle-timeout.test.ts
index 41b5e2f121b..de03d8244fb 100644
--- a/src/agents/pi-embedded-runner/run/llm-idle-timeout.test.ts
+++ b/src/agents/pi-embedded-runner/run/llm-idle-timeout.test.ts
@@ -100,6 +100,17 @@ describe("resolveLlmIdleTimeoutMs", () => {
     "http://192.168.1.20:11434",
     "http://100.64.0.5:11434",
     "http://100.127.255.254:11434",
+    // RFC 4193 IPv6 unique local (Tailscale IPv6 mesh fd7a:115c:a1e0::/48
+    // falls inside fc00::/7).
+    "http://[fc00::1]:11434",
+    "http://[fd00::1]:11434",
+    "http://[fd7a:115c:a1e0::dead:beef]:11434",
+    "http://[fdff:ffff:ffff:ffff:ffff:ffff:ffff:ffff]:11434",
+    // RFC 4291 IPv6 link-local.
+    "http://[fe80::1]:11434",
+    "http://[fe9a::1]:11434",
+    "http://[feab:cd::1]:11434",
+    "http://[febf::1]:11434",
   ])("disables the default idle watchdog for local provider baseUrl %s", (baseUrl) => {
     expect(resolveLlmIdleTimeoutMs({ model: { baseUrl } })).toBe(0);
   });
@@ -113,6 +124,25 @@ describe("resolveLlmIdleTimeoutMs", () => {
     expect(resolveLlmIdleTimeoutMs({ model: { baseUrl } })).toBe(DEFAULT_LLM_IDLE_TIMEOUT_MS);
   });
 
+  it.each([
+    // Just outside fc00::/7 (fe.. and 00fc::/16 are not unique-local).
+    "http://[fec0::1]:11434",
+    "http://[fbff::1]:11434",
+    // Just outside fe80::/10 (fec0:: was deprecated site-local, fe7f:: not LL).
+    "http://[fe7f::1]:11434",
+    // Public IPv6.
+    "http://[2001:db8::1]:11434",
+    // Abbreviated `fc::1` expands to 00fc:0:0:...:1, first byte is 0x00, not
+    // 0xfc — outside fc00::/7. Strict first-hextet match keeps this remote.
+    "http://[fc::1]:11434",
+    // IPv4-mapped IPv6 outside loopback (private RFC 1918 in mapped form is
+    // intentionally not matched, mirroring the SSRF policy helper).
+    "http://[::ffff:10.0.0.5]:11434",
+    "http://[::ffff:192.168.1.20]:11434",
+  ])("keeps the default idle watchdog for non-private IPv6 baseUrl %s", (baseUrl) => {
+    expect(resolveLlmIdleTimeoutMs({ model: { baseUrl } })).toBe(DEFAULT_LLM_IDLE_TIMEOUT_MS);
+  });
+
   it.each([
     "http://10.0.0.5evil:11434",
     "http://127.0.0.1foo:11434",
diff --git a/src/agents/pi-embedded-runner/run/llm-idle-timeout.ts b/src/agents/pi-embedded-runner/run/llm-idle-timeout.ts
index 18d1c8ddf19..a282ce90801 100644
--- a/src/agents/pi-embedded-runner/run/llm-idle-timeout.ts
+++ b/src/agents/pi-embedded-runner/run/llm-idle-timeout.ts
@@ -20,6 +20,24 @@ const MAX_SAFE_TIMEOUT_MS = 2_147_000_000;
  * (Ollama, LM Studio, llama.cpp) legitimately stay silent for many minutes
  * during prompt evaluation and thinking, so the network-silence-as-hang
  * heuristic that motivates the default idle watchdog does not apply.
+ *
+ * Coverage scope:
+ *  - IPv4 loopback (RFC 5735, full 127/8), RFC 1918 private, RFC 6598 shared
+ *    CGNAT (100.64/10 — Tailscale/Headscale IPv4 mesh), `0.0.0.0`, `localhost`,
+ *    and `*.local` mDNS (RFC 6762).
+ *  - IPv6 loopback `::1`, IPv6 unique local `fc00::/7` (RFC 4193 — Tailscale's
+ *    IPv6 mesh `fd7a:115c:a1e0::/48` falls in this range), and IPv6 link-local
+ *    `fe80::/10` (RFC 4291).
+ *  - IPv4-mapped IPv6 covers loopback only (`::ffff:127.0.0.1`,
+ *    `::ffff:7f00:1`); private IPv4 in mapped form is intentionally not
+ *    matched, mirroring the SSRF-policy helper in
+ *    `src/cron/isolated-agent/model-preflight.runtime.ts`.
+ *  - DNS-resolved local aliases (e.g. an `/etc/hosts` entry mapping a custom
+ *    hostname to a private IP) are not detected: classification keys on
+ *    `URL.hostname` so resolution would have to happen here, and adding
+ *    sync/async DNS to the watchdog hot path is disproportionate. Affected
+ *    users can use the IP directly or set
+ *    `models.providers.<id>.timeoutSeconds` explicitly.
  */
 function isLocalProviderBaseUrl(baseUrl: string): boolean {
   let host: string;
@@ -41,6 +59,15 @@ function isLocalProviderBaseUrl(baseUrl: string): boolean {
   ) {
     return true;
   }
+  // IPv6 unique local (RFC 4193, fc00::/7) and link-local (RFC 4291,
+  // fe80::/10). The full first hextet is required so an abbreviated `fc::1`
+  // (which expands to `00fc:0:0:...` and is therefore not in fc00::/7)
+  // correctly stays on the cloud path. The first regex requires four hex
+  // digits then a colon; a zone identifier such as `fe80::1%eth0` is fine
+  // because the prefix still matches at the start.
+  if (/^f[cd][0-9a-f]{2}:/.test(host) || /^fe[89ab][0-9a-f]:/.test(host)) {
+    return true;
+  }
   // Require a strict IPv4 literal before parsing; `Number.parseInt` is
   // permissive and would otherwise let `10.0.0.5evil` parse to [10,0,0,5]
   // and disable the watchdog for a non-IP hostname.