diff --git a/src/services/biometricAvailability.ts b/src/services/biometricAvailability.ts
new file mode 100644
index 0000000..7dbe32a
--- /dev/null
+++ b/src/services/biometricAvailability.ts
@@ -0,0 +1,50 @@
+/**
+ * Typed biometric availability reporting. (#784)
+ *
+ * Biometric login surfaced every failure as the same generic "not available"
+ * Error, so callers could not tell unsupported hardware from an unenrolled
+ * device and always showed the same dead-end message. These helpers classify
+ * the blocking reason and carry it on a typed, `instanceof`-checkable error.
+ * The caller passes in probe results, keeping this testable without natives.
+ */
+
+export type BiometricUnavailableReason =
+  | 'noHardware'
+  | 'notEnrolled'
+  | 'notEnabled'
+  | 'unknown';
+
+const REASON_MESSAGES: Record<BiometricUnavailableReason, string> = {
+  noHardware: 'This device has no biometric sensor.',
+  notEnrolled: 'No fingerprint or face is enrolled. Add one in device settings.',
+  notEnabled: 'Biometric login is off. Turn it on in app settings.',
+  unknown: 'Biometric authentication is unavailable on this device.',
+};
+
+/** Error carrying the specific reason biometric login could not run. */
+export class BiometricUnavailableError extends Error {
+  readonly code = 'BIOMETRIC_UNAVAILABLE';
+  readonly reason: BiometricUnavailableReason;
+
+  constructor(reason: BiometricUnavailableReason) {
+    super(REASON_MESSAGES[reason]);
+    this.name = 'BiometricUnavailableError';
+    this.reason = reason;
+  }
+}
+
+export interface BiometricProbe {
+  hasHardware: boolean;
+  isEnrolled: boolean;
+  isEnabledInApp: boolean;
+}
+
+/** Returns the blocking reason, or null when biometric login may proceed. */
+export function getBiometricUnavailableReason(
+  probe: BiometricProbe
+): BiometricUnavailableReason | null {
+  if (!probe.hasHardware) return 'noHardware';
+  if (!probe.isEnrolled) return 'notEnrolled';
+  if (!probe.isEnabledInApp) return 'notEnabled';
+  return null;
+}
diff --git a/src/services/pushChannelSetup.ts b/src/services/pushChannelSetup.ts
new file mode 100644
index 0000000..1b044b2
--- /dev/null
+++ b/src/services/pushChannelSetup.ts
@@ -0,0 +1,48 @@
+/**
+ * Android notification channel setup with retry and visible failure. (#785)
+ *
+ * Channel creation was wrapped in a bare try/catch that swallowed the error,
+ * so Android notifications silently never appeared and nothing in the logs
+ * said why. This retries once — channel creation fails transiently during
+ * cold start — and reports the failure instead of continuing quietly.
+ */
+
+export interface ChannelSetupResult {
+  ok: boolean;
+  attempts: number;
+  error?: Error;
+}
+
+type CreateChannel = () => Promise<void>;
+type ReportFailure = (message: string, error: Error) => void;
+
+const MAX_ATTEMPTS = 2;
+
+/**
+ * Runs `createChannel`, retrying once on failure.
+ *
+ * Never throws: startup should continue deliberately rather than crash, so the
+ * outcome is returned and the failure is handed to `reportFailure` (Sentry in
+ * production, a visible warning in dev).
+ */
+export async function setUpNotificationChannel(
+  createChannel: CreateChannel,
+  reportFailure: ReportFailure
+): Promise<ChannelSetupResult> {
+  let lastError = new Error('Notification channel setup did not run.');
+
+  for (let attempt = 1; attempt <= MAX_ATTEMPTS; attempt++) {
+    try {
+      await createChannel();
+      return { ok: true, attempts: attempt };
+    } catch (caught) {
+      lastError = caught instanceof Error ? caught : new Error(String(caught));
+    }
+  }
+
+  reportFailure(
+    `Android notification channel setup failed after ${MAX_ATTEMPTS} attempts.`,
+    lastError
+  );
+  return { ok: false, attempts: MAX_ATTEMPTS, error: lastError };
+}
diff --git a/src/services/sessionInvalidation.ts b/src/services/sessionInvalidation.ts
new file mode 100644
index 0000000..111c35b
--- /dev/null
+++ b/src/services/sessionInvalidation.ts
@@ -0,0 +1,50 @@
+/**
+ * Session invalidation sequence. (#786)
+ *
+ * After three consecutive 401s the refresh path cleared tokens and stopped
+ * there, leaving the socket connected and the user on an authenticated
+ * screen. This runs the remaining steps, never letting one failure stop them.
+ */
+
+export const SESSION_INVALIDATED = 'SESSION_INVALIDATED' as const;
+
+export interface SessionInvalidationSteps {
+  clearTokens: () => Promise<void> | void;
+  disconnectSocket: () => Promise<void> | void;
+  navigateToLogin: () => Promise<void> | void;
+  notify?: (event: typeof SESSION_INVALIDATED) => void;
+}
+
+export interface SessionInvalidationOutcome {
+  completed: string[];
+  failed: string[];
+}
+
+/**
+ * Executes every logout step, continuing past individual failures so a broken
+ * socket teardown cannot strand the user on an authenticated screen.
+ */
+export async function invalidateSession(
+  steps: SessionInvalidationSteps
+): Promise<SessionInvalidationOutcome> {
+  const ordered: [string, () => Promise<void> | void][] = [
+    ['clearTokens', steps.clearTokens],
+    ['disconnectSocket', steps.disconnectSocket],
+    ['navigateToLogin', steps.navigateToLogin],
+  ];
+
+  const completed: string[] = [];
+  const failed: string[] = [];
+
+  for (const [name, run] of ordered) {
+    try {
+      await run();
+      completed.push(name);
+    } catch {
+      failed.push(name);
+    }
+  }
+
+  steps.notify?.(SESSION_INVALIDATED);
+  return { completed, failed };
+}
diff --git a/src/utils/conflictPayload.ts b/src/utils/conflictPayload.ts
new file mode 100644
index 0000000..e9dd3d9
--- /dev/null
+++ b/src/utils/conflictPayload.ts
@@ -0,0 +1,44 @@
+/**
+ * 409 Conflict payload parsing. (#787)
+ *
+ * Conflicts were logged as raw response bodies, so the UI had nothing typed
+ * to drive a resolution prompt and the user saw a generic error with no way
+ * to resolve it. This normalises the shapes the API returns into one payload
+ * ConflictResolutionModal can consume.
+ */
+
+export interface ConflictPayload {
+  resource: string;
+  serverVersion: string | null;
+  clientVersion: string | null;
+}
+
+/** First readable string/number among `keys`, or null. */
+function readString(source: Record<string, unknown>, ...keys: string[]): string | null {
+  for (const key of keys) {
+    const value = source[key];
+    if (typeof value === 'string' && value.trim()) return value;
+    if (typeof value === 'number') return String(value);
+  }
+  return null;
+}
+
+/**
+ * Returns a typed conflict payload, or null when `data` carries no
+ * recognisable conflict details — the caller should then fall back to the
+ * generic error path rather than opening an empty resolution modal.
+ */
+export function parseConflictPayload(data: unknown): ConflictPayload | null {
+  if (!data || typeof data !== 'object') return null;
+  const source = data as Record<string, unknown>;
+
+  const serverVersion = readString(source, 'serverVersion', 'server_version', 'currentVersion');
+  const clientVersion = readString(source, 'clientVersion', 'client_version', 'submittedVersion');
+  if (!serverVersion && !clientVersion) return null;
+
+  return {
+    resource: readString(source, 'resource', 'entity', 'type') ?? 'record',
+    serverVersion,
+    clientVersion,
+  };
+}