Phase C+9 — XamContentCreateEnumerator canary-parity X_ERROR_NO_SUCH_USER
=========================================================================

Scope: `crates/xenia-kernel/src/xam.rs`
LOC: ~85 body + ~125 test = ~210 net additive

Registration change — xam.rs:59:
--------------------------------

-    state.register_export(Xam, 0x025C, "XamContentCreateEnumerator", stub_success);
+    state.register_export(Xam, 0x025C, "XamContentCreateEnumerator", xam_content_create_enumerator);

Body — new function after `xam_user_get_signin_state` (xam.rs:384):
-------------------------------------------------------------------

+ // ===== Content =====
+
+ /// `XamContentCreateEnumerator(user_index, device_id, content_type,
+ /// content_flags, items_per_enumerate, buffer_size_ptr, handle_out)`.
+ /// Mirrors xenia-canary `XamContentCreateEnumerator_entry`
+ /// (xam_content.cc:129-220). Reading-error #28 discipline applied: body
+ /// shape verified against canary source.
+ ///
+ /// Canary's normal-path success returns `X_ERROR_SUCCESS` (0) with a
+ /// fresh enumerator handle in `*handle_out`. The Phase A oracle at
+ /// `tid_event_idx=102197` shows canary returning `X_ERROR_NO_SUCH_USER`
+ /// (`0x525`, 1317) with empty side_effects — the call hit the
+ /// `if (!user) return X_ERROR_NO_SUCH_USER;` early-return at
+ /// xam_content.cc:153-155 because no profile is installed in canary's
+ /// default `--mute=true` config (no `--profile_slot_*` flags).
+ ///
+ /// Ours has no profile-manager state, so all `user_index != 0xFE`
+ /// queries miss. Mirror the early-return: write `*buffer_size_ptr` per
+ /// canary line 145-147 (which executes *before* the user check) and
+ /// return `X_ERROR_NO_SUCH_USER`. Implementing real content enumeration
+ /// is an XAM-content-subsystem session (escalation-tier scope), not
+ /// this fix.
+ ///
+ /// Side note on internal consistency: ours's `xam_user_get_signin_state`
+ /// returns 1 for `user_index == 0`, conflicting with the "no profile"
+ /// model used here. That divergence surfaces later in the Phase A trace
+ /// (idx 107996+) and is a separate fix — deferred per single-fix
+ /// discipline.
+ fn xam_content_create_enumerator(
+     ctx: &mut PpcContext,
+     mem: &GuestMemory,
+     _state: &mut KernelState,
+ ) {
+     const X_USER_INDEX_NONE: u32 = 0xFE;
+     const X_USER_INDEX_LATEST: u32 = 0xFD;
+     const X_USER_MAX_USER_COUNT: u32 = 4;
+     const X_E_INVALIDARG: u32 = 0x8007_0057;
+     const X_ERROR_NO_SUCH_USER: u32 = 0x0000_0525;
+     const X_ERROR_SUCCESS: u32 = 0;
+     const X_CONTENT_DATA_SIZE: u32 = 0x134;
+
+     let user_index = ctx.gpr[3] as u32;
+     let device_id = ctx.gpr[4] as u32;
+     let _content_type = ctx.gpr[5] as u32;
+     let _content_flags = ctx.gpr[6] as u32;
+     let items_per_enumerate = ctx.gpr[7] as u32;
+     let buffer_size_ptr = ctx.gpr[8] as u32;
+     let handle_out = ctx.gpr[9] as u32;
+
+     let device_unknown = device_id != 0 && device_id > 2;
+     if device_unknown || handle_out == 0 {
+         if buffer_size_ptr != 0 {
+             mem.write_u32(buffer_size_ptr, 0);
+         }
+         ctx.gpr[3] = X_E_INVALIDARG as u64;
+         return;
+     }
+
+     if buffer_size_ptr != 0 {
+         mem.write_u32(buffer_size_ptr, X_CONTENT_DATA_SIZE.wrapping_mul(items_per_enumerate));
+     }
+
+     if user_index != X_USER_INDEX_NONE {
+         let out_of_range = user_index >= X_USER_MAX_USER_COUNT
+             && user_index != X_USER_INDEX_LATEST;
+         let _ = out_of_range; // documentation only — both branches → no user
+         ctx.gpr[3] = X_ERROR_NO_SUCH_USER as u64;
+         return;
+     }
+
+     if handle_out != 0 {
+         mem.write_u32(handle_out, 0);
+     }
+     ctx.gpr[3] = X_ERROR_SUCCESS as u64;
+ }

Tests — 5 new in `mod tests`:
-----------------------------

+ xam_content_create_enumerator_returns_no_such_user_for_user0
+ xam_content_create_enumerator_invalid_handle_out_returns_invalidarg
+ xam_content_create_enumerator_unknown_device_returns_invalidarg
+ xam_content_create_enumerator_user_none_returns_success
+ xam_content_create_enumerator_out_of_range_user_returns_no_such_user

The first test is the THE Phase A oracle case: user_index=0,
device_id=1 (HDD), items_per_enumerate=4 → asserts ret=0x525 and
buffer_size_ptr=0x134*4 (canary writes size BEFORE the user check).