diff --git a/src/core/__tests__/api-provider-models.test.ts b/src/core/__tests__/api-provider-models.test.ts
index 6043831..aabeab2 100644
--- a/src/core/__tests__/api-provider-models.test.ts
+++ b/src/core/__tests__/api-provider-models.test.ts
@@ -217,3 +217,25 @@ test("fetchProviderModels redacts provider errors", async () => {
   assert.equal(result.kind, "auth_failed");
   assert.equal(result.detail, "invalid key [redacted]");
 });
+
+test("fetchProviderModels classifies 403 provider responses as forbidden", async () => {
+  const result = await fetchProviderModels(
+    resolveSessionRuntimeAuthConfig({
+      session_auth_mode: "anthropic-api-key",
+      agent_api_protocol: "openai",
+      agent_model: "restricted-model",
+      agent_base_url: "https://api.openai.com/v1",
+      anthropic_api_key: "sk-openai-secret",
+    }),
+    {
+      fetchImpl: async () =>
+        jsonResponse(403, {
+          error: { message: "model list is not enabled for this account" },
+        }),
+    },
+  );
+
+  assert.equal(result.ok, false);
+  if (result.ok) return;
+  assert.equal(result.kind, "forbidden");
+});
diff --git a/src/core/__tests__/api-provider-runtime.test.ts b/src/core/__tests__/api-provider-runtime.test.ts
index 763c022..c68bc07 100644
--- a/src/core/__tests__/api-provider-runtime.test.ts
+++ b/src/core/__tests__/api-provider-runtime.test.ts
@@ -1,6 +1,7 @@
 import { test } from "node:test";
 import assert from "node:assert/strict";
 import {
+  buildProviderChatRequest,
   runProviderChatCompletion,
   validateProviderRuntimeConfig,
 } from "../api-provider-runtime";
@@ -60,6 +61,45 @@ test("runProviderChatCompletion posts OpenAI-compatible chat history", async ()
   });
 });
 
+test("buildProviderChatRequest preserves existing versioned OpenAI-compatible base paths", () => {
+  const request = buildProviderChatRequest(
+    resolveSessionRuntimeAuthConfig({
+      session_auth_mode: "anthropic-api-key",
+      agent_api_protocol: "openai",
+      agent_model: "proxy-model",
+      agent_base_url: "https://proxy.example.com/v2",
+      anthropic_api_key: "sk-proxy-test",
+    }),
+    new URL("https://proxy.example.com/v2"),
+    [{ role: "user", content: "Use proxy" }],
+  );
+
+  assert.equal(request.url, "https://proxy.example.com/v2/chat/completions");
+});
+
+test("runProviderChatCompletion classifies 403 provider responses as forbidden", async () => {
+  const result = await runProviderChatCompletion(
+    resolveSessionRuntimeAuthConfig({
+      session_auth_mode: "anthropic-api-key",
+      agent_api_protocol: "openai",
+      agent_model: "restricted-model",
+      agent_base_url: "https://api.openai.com/v1",
+      anthropic_api_key: "sk-openai-test",
+    }),
+    [{ role: "user", content: "Use restricted model" }],
+    {
+      fetchImpl: async () =>
+        jsonResponse(403, {
+          error: { message: "model not enabled for this account" },
+        }),
+    },
+  );
+
+  assert.equal(result.ok, false);
+  if (result.ok) return;
+  assert.equal(result.kind, "forbidden");
+});
+
 test("validateProviderRuntimeConfig allows loopback Ollama without an API key", () => {
   const result = validateProviderRuntimeConfig(
     resolveSessionRuntimeAuthConfig({
@@ -133,3 +173,19 @@ test("validateProviderRuntimeConfig allows Azure OpenAI hosts", () => {
 
   assert.equal(result.ok, true);
 });
+
+test("validateProviderRuntimeConfig blocks IPv4-mapped IPv6 private hosts", () => {
+  const result = validateProviderRuntimeConfig(
+    resolveSessionRuntimeAuthConfig({
+      session_auth_mode: "anthropic-api-key",
+      agent_api_protocol: "openai",
+      agent_model: "gpt-4o-mini",
+      agent_base_url: "https://[::ffff:192.168.1.1]/v1",
+      anthropic_api_key: "sk-test",
+    }),
+  );
+
+  assert.equal(result.ok, false);
+  if (result.ok) return;
+  assert.match(result.error, /Internal API hosts are blocked/);
+});
diff --git a/src/core/__tests__/api-session-runtime.test.ts b/src/core/__tests__/api-session-runtime.test.ts
index 0817ea6..2b45fae 100644
--- a/src/core/__tests__/api-session-runtime.test.ts
+++ b/src/core/__tests__/api-session-runtime.test.ts
@@ -137,7 +137,7 @@ test("runProviderSessionTurn fails before recording a user message when the brow
   );
 });
 
-test("runProviderSessionTurn does not save provider output after the session is killed", async () => {
+test("runProviderSessionTurn removes the pending user message after the session is killed", async () => {
   const db = makeTestDb();
   const events: ChatStreamEvent[] = [];
 
@@ -181,7 +181,7 @@ test("runProviderSessionTurn does not save provider output after the session is
         "SELECT role, content FROM session_messages WHERE session_id = ? ORDER BY id ASC",
       )
       .all("session-killed"),
-    [{ role: "user", content: "Stop before output" }],
+    [],
   );
   assert.equal(
     (
diff --git a/src/core/agent-settings.ts b/src/core/agent-settings.ts
index ca4e7dc..679a77e 100644
--- a/src/core/agent-settings.ts
+++ b/src/core/agent-settings.ts
@@ -563,6 +563,7 @@ export function getBrowserApiKeyScope(
 ): string {
   const apiProtocol = sanitizeApiProtocol(settings.apiProtocol);
   const apiBaseUrl = sanitizeApiBaseUrl(settings.apiBaseUrl, apiProtocol);
+  // Use a delimiter that cannot appear in sanitized protocol names or URLs.
   return `${apiProtocol}\n${apiBaseUrl}`;
 }
 
diff --git a/src/core/api-provider-models.ts b/src/core/api-provider-models.ts
index a901dbe..0edf03d 100644
--- a/src/core/api-provider-models.ts
+++ b/src/core/api-provider-models.ts
@@ -182,7 +182,7 @@ function appendVersionedApiPath(
   const url = new URL(baseUrl.toString());
   const basePath = url.pathname.replace(/\/+$/, "");
   const normalizedSuffix = suffix.startsWith("/") ? suffix : `/${suffix}`;
-  url.pathname = basePath.endsWith(`/${version}`)
+  url.pathname = /\/v\d+(?:beta)?$/.test(basePath)
     ? `${basePath}${normalizedSuffix}`
     : `${basePath}/${version}${normalizedSuffix}`;
   return url.toString();
@@ -260,7 +260,8 @@ function classifyProviderFailure(
   status: number,
   detail: string | undefined,
 ): ProviderRuntimeFailureKind {
-  if (status === 401 || status === 403) return "auth_failed";
+  if (status === 401) return "auth_failed";
+  if (status === 403) return "forbidden";
   if (status === 429) return "rate_limited";
   if (status >= 500) return "upstream_unavailable";
   if (status === 404) return "not_found_model";
diff --git a/src/core/api-provider-runtime.ts b/src/core/api-provider-runtime.ts
index 2008f3c..4ac74d5 100644
--- a/src/core/api-provider-runtime.ts
+++ b/src/core/api-provider-runtime.ts
@@ -74,6 +74,36 @@ function parseIpv4(hostname: string): [number, number, number, number] | null {
   return parsed as [number, number, number, number];
 }
 
+function parseIpv4MappedIpv6(
+  hostname: string,
+): [number, number, number, number] | null {
+  const mappedPrefixes = ["::ffff:", "0:0:0:0:0:ffff:"];
+  const prefix = mappedPrefixes.find((candidate) =>
+    hostname.startsWith(candidate),
+  );
+  if (!prefix) return null;
+
+  const suffix = hostname.slice(prefix.length);
+  const dotted = parseIpv4(suffix);
+  if (dotted) return dotted;
+
+  const parts = suffix.split(":");
+  if (parts.length !== 2) return null;
+  const words = parts.map((part) => {
+    if (!/^[0-9a-f]{1,4}$/i.test(part)) return null;
+    return Number.parseInt(part, 16);
+  });
+  if (words.some((word) => word === null)) return null;
+  const [high, low] = words as [number, number];
+  return [high >> 8, high & 0xff, low >> 8, low & 0xff];
+}
+
+function parseIpv6FirstGroup(hostname: string): number | null {
+  const firstGroup = hostname.split(":", 1)[0];
+  if (!/^[0-9a-f]{1,4}$/i.test(firstGroup)) return null;
+  return Number.parseInt(firstGroup, 16);
+}
+
 function normalizeHost(hostname: string): string {
   const stripped = hostname.startsWith("[") && hostname.endsWith("]")
     ? hostname.slice(1, -1)
@@ -85,12 +115,15 @@ export function isLoopbackHost(hostname: string): boolean {
   const host = normalizeHost(hostname);
   if (host === "localhost" || host === "::1") return true;
   const ipv4 = parseIpv4(host);
-  return Boolean(ipv4 && ipv4[0] === 127);
+  const mappedIpv4 = parseIpv4MappedIpv6(host);
+  return Boolean(
+    (ipv4 && ipv4[0] === 127) || (mappedIpv4 && mappedIpv4[0] === 127),
+  );
 }
 
 function isBlockedExternalHost(hostname: string): boolean {
   const host = normalizeHost(hostname);
-  const ipv4 = parseIpv4(host);
+  const ipv4 = parseIpv4(host) ?? parseIpv4MappedIpv6(host);
   if (ipv4) {
     const [a, b] = ipv4;
     return (
@@ -103,7 +136,13 @@ function isBlockedExternalHost(hostname: string): boolean {
       a >= 224
     );
   }
-  return host === "::" || /^f[cd][0-9a-f]{2}:/i.test(host) || /^fe[89ab][0-9a-f]:/i.test(host);
+  const firstGroup = parseIpv6FirstGroup(host);
+  return (
+    host === "::" ||
+    (firstGroup !== null &&
+      ((firstGroup & 0xfe00) === 0xfc00 ||
+        (firstGroup & 0xffc0) === 0xfe80))
+  );
 }
 
 export function validateAgentConnectionBaseUrl(baseUrl: string): ParsedBaseUrl {
@@ -419,7 +458,7 @@ function appendVersionedApiPath(baseUrl: URL, suffix: string): string {
   const url = new URL(baseUrl.toString());
   const basePath = url.pathname.replace(/\/+$/, "");
   const normalizedSuffix = suffix.startsWith("/") ? suffix : `/${suffix}`;
-  url.pathname = basePath.endsWith("/v1")
+  url.pathname = /\/v\d+(?:beta)?$/.test(basePath)
     ? `${basePath}${normalizedSuffix}`
     : `${basePath}/v1${normalizedSuffix}`;
   return url.toString();
@@ -538,7 +577,8 @@ function classifyProviderFailure(
   status: number,
   detail: string | undefined,
 ): ProviderRuntimeFailureKind {
-  if (status === 401 || status === 403) return "auth_failed";
+  if (status === 401) return "auth_failed";
+  if (status === 403) return "forbidden";
   if (status === 429) return "rate_limited";
   if (status >= 500) return "upstream_unavailable";
   if (status === 404) return "not_found_model";
diff --git a/src/core/api-session-runtime.ts b/src/core/api-session-runtime.ts
index 80b263b..ac5a4c5 100644
--- a/src/core/api-session-runtime.ts
+++ b/src/core/api-session-runtime.ts
@@ -91,7 +91,7 @@ export async function runProviderSessionTurn({
     return { ok: false, error: validated.error };
   }
 
-  db.prepare(
+  const insertedUser = db.prepare(
     "INSERT INTO session_messages (session_id, role, content) VALUES (?, 'user', ?)",
   ).run(sessionId, message);
   emit(sessionId, { type: "message", role: "user", content: message });
@@ -107,6 +107,9 @@ export async function runProviderSessionTurn({
   });
   const postRequestStatus = getStoredSessionStatus(db, sessionId);
   if (postRequestStatus !== "running") {
+    db.prepare(
+      "DELETE FROM session_messages WHERE id = ? AND session_id = ? AND role = 'user'",
+    ).run(insertedUser.lastInsertRowid, sessionId);
     return {
       ok: false,
       error: `Provider response ignored because the session is ${postRequestStatus ?? "missing"}.`,