fix(rocm/gemma4): #838 widen indexed MoE gate to T<=63 + retirement-safe dispatch

.agents/claims/CLAIM-ROCM-GEMMA4-INDEXED-MAX-T.md

@@ -0,0 +1,5 @@
+# CLAIM-ROCM-GEMMA4-INDEXED-MAX-T
+
+| Claim | Row IDs | Agent | Worktree | Branch | Owned scope | State | Last update |
+|---|---|---|---|---|---|---|---|
+| `CLAIM-ROCM-GEMMA4-INDEXED-MAX-T` | `BACKEND-ROCM` (slug `ROCM-GEMMA4-INDEXED-MAX-T`, issue #838) | hermes-vllm (lab), helper | `/home/don/llms/vllm.cpp-indexed-max-t` | `row/ROCM-GEMMA4-INDEXED-MAX-T` | Owns ONLY: widen `gemma4_moe.cpp` T==1 indexed gate to T≤63 via `VT_GEMMA4_DECODE_INDEXED_MAX_T` default 63, using existing per-token indexed helpers, plus tensor oracle vs serial reference. **EXCLUDED:** packed `ExpertGeGLUFp8TopKIndexedBatched`, DEVICE_GROUP, INDEXED_NOSYNC, #837, #839, #697. Independent history from abandoned `row/ROCM-GEMMA4-XDEV-MOE`. | `IMPLEMENTING` | 2026-08-15 — d973/0f32 repair: retire inside acc_idx scope, Retire fail-closed, independent serial ref, injectable arms, owner kind |

.agents/issue-index.md

@@ -453,3 +453,4 @@ rather than merged. `scripts/check-agent-record.py` gates both.
 | [#1353](https://github.com/mudler/vllm.cpp/issues/1353) | `ENG-RECORD-ANCHOR-RATCHET` | A full disk makes `scripts/agent-preflight.sh` report record and policy defects that do not exist. Measured at `63ff58272` with 896M free of 447G: ten suites go red together — `test_check_release_binary_contract`, `test_release_postpublish_audit`, `test_check_container_matrix`, `test_release_index`, `test_release_metadata`, `test_release_accelerator_metadata`, `test_release_macos_metadata`, `test_release_windows_metadata`, `test_agent_role`, `test_agent_onboard` — and the trailing summary names all ten without mentioning the disk. The cause appears only inside one suite's captured output several screens up (`error: copy-fd: write returned: No space left on device`), interleaved with fixture failures that read exactly like findings (`ERROR: x: see (#157) and #174`, `ERROR: x: landed without a row PR`). All ten build a scratch git repository in a temporary directory, so all ten fail together and all ten fail toward a verdict about RECORDS rather than about the environment — the `.agents/verification.md` broken-instrument shape, and an agent reading it has every reason to start repairing records that were never broken. Reclaiming 2.7G of one row's own build tree and re-running the identical command turned all ten green with no tree change (`86 gates, 86 ok, 0 FAIL, 0 SKIP`, exit 0). The fix is a precondition, not a suppression: check free space before the suites that need a scratch repository and refuse naming the disk, exactly as `test_cpu_x86_llamacpp_floor` refuses to measure under contention ([#618](https://github.com/mudler/vllm.cpp/issues/618)). A gate that cannot run must say so rather than return a verdict. Found while landing [#1332](https://github.com/mudler/vllm.cpp/issues/1332) M0+M1 and NOT fixed in that flow, because it changes preflight semantics and adds a refusal path, which `AGENTS.md` routes to the normal row, spec and fresh-review path | bug |
 | [#1376](https://github.com/mudler/vllm.cpp/issues/1376) | `ENG-CUDAGRAPH-BREAK` | `main` was red on `tests/scripts/test_check_gate_commands.py`, measured at `601b576c6` in a detached worktree of `origin/main`: 8 failures of 44 tests, every one a comparison between the computed runnable population and `RUNNABLE_BASELINE`. `ENG-CUDAGRAPH-BREAK` was in the first and absent from the second. Cause: W5 of that row ([#1361](https://github.com/mudler/vllm.cpp/issues/1361)) filled its spec's `## Gates` section with runnable evidence, including a named test binary with its case and assertion counts and an exit status, which is exactly what moves a row into the runnable population. The ratchet's own error text instructs a re-pin in the SAME change, and the re-pin was not made. This is the growth case the ratchet exists to force a decision about, not a defect in that row's work. **It landed with no remote verdict**: the continuous integration lane that would have caught it independently has not executed for this repository since roughly 07:43Z on 19 August 2026, with runs queueing and none starting while GitHub reports Actions operational. FIXED IN FLOW while merging `origin/main` into `row/ENG-HF-MODEL-DOWNLOAD` for [#1280](https://github.com/mudler/vllm.cpp/issues/1280), because the fix is small and clear and a red `main` blocks every other row's gate. The entry is added with a justifying comment in the form the neighbouring entries use, no checker semantics change, and no test is weakened. After the re-pin the suite reports 45 tests OK and the audit reads 39 runnable of 119 gated rows | bug |
 | [#1375](https://github.com/mudler/vllm.cpp/issues/1375) | `MODEL-DIFFUSION-LTX25` | First end-to-end per-forward cost for the FULL 21.004 B LTX-2.5 DiT on GB10, measured on run `20260819T150230Z` with binary `0a43a750` built from [`7b9e207b1`](https://github.com/mudler/vllm.cpp/commit/7b9e207b1) (#1252). At 1024x576/25f (2304 latent tokens) the governor resolved **7 forward starts from the GPU busy/idle edge counter** and measured `per_forward ~162.0 s` with `first_dit = 481.5 s`, so the recipe's fixed 60 forwards (30 steps x 2 CFG legs, `ltx2_pipeline.cpp:521-529`) project **10 803 s against the rung's 7 153 s budget** and the rung was refused rather than run to the wall. The same lease then COMPLETED 768x448/25f (1344 tokens) in 2990 s, so the ceiling is geometry against lease length, not a defect. TWO instrument facts belong with the number, because both have already caused a wrong reading: `gpu_edges=0` means the GPU never went idle long enough to sample an edge (SATURATED), not that no work ran — this rung sampled 85% of 3191 samples above 50% utilisation; and `eu-stack` resolves no frames in the rc worker container, so phase attribution came from the cpu%/rss signature rather than from symbols. Owned by the LTX-2.5 row; spec [`ltx-2-5.md`](specs/ltx-2-5.md) | measurement |
+| [#838](https://github.com/mudler/vllm.cpp/issues/838) | `ROCM-GEMMA4-INDEXED-MAX-T` | Gemma4 indexed MoE gate widened to T<=63 with injectable dispatch + retire-in-scope | perf |

.agents/specs/rocm-gemma4-indexed-max-t-donor-gate-911-933.log

@@ -0,0 +1,23 @@
+  // Device-indexed FP8 MoE for small packed T — no router D2H, no host top-k gather.
+  // T=1: original KEEP decode path (hipGraph-stable TLS acc).
+  // T=2..min(MAX, batch_min-1): P1 concurrent-decode gap (research 2026-08-11).
+  // VT_GEMMA4_DECODE_INDEXED_MAX_T: default 63; =1 → T=1 only; clamp [1,63].
+  static const int64_t kDecodeIndexedMaxT = []() -> int64_t {
+    const char* e = std::getenv("VT_GEMMA4_DECODE_INDEXED_MAX_T");
+    if (e == nullptr || !e[0]) return 63;
+    const long v = std::strtol(e, nullptr, 10);
+    if (v < 1) return 1;
+    if (v > 63) return 63;
+    return static_cast<int64_t>(v);
+  }();
+  // P0 overlap enabler (default OFF): keep the enqueue-only indexed path for
+  // prefill T so layer-split does not hipStreamSynchronize after router D2H.
+  // Not a KEEP speed path — per-token launches. Cap 8192 (pipe ubatch).
+  static const int64_t kPrefillIndexedNoSyncMaxT = []() -> int64_t {
+    const char* e = std::getenv("VT_GEMMA4_PREFILL_INDEXED_NOSYNC");
+    if (!e || e[0] != '1') return 0;
+    return 8192;
+  }();
+  const int64_t indexed_max_t =
+      (kPrefillIndexedNoSyncMaxT > kDecodeIndexedMaxT) ? kPrefillIndexedNoSyncMaxT
+                                                      : kDecodeIndexedMaxT;

.agents/specs/rocm-gemma4-indexed-max-t-donor-ok-1088-1110.log

@@ -0,0 +1,23 @@
+    }
+    static std::atomic<int> grp_fail{0};
+    if (grp_fail.fetch_add(1) < 4) {
+      std::fprintf(stderr, "gemma4 moe: device-group FAIL T=%lld — falling back\n",
+                   static_cast<long long>(T));
+      std::fflush(stderr);
+    }
+  }
+  const bool indexed_ok_t =
+      (T >= 1 && T <= indexed_max_t && top_k <= 8 && top_k > 0 && fp8_res &&
+       (kPrefillIndexedNoSyncMaxT > 0 || T < kPrefillBatchMinT));
+  // Indexed only while T is below the group-by-expert crossover (unless nosync).
+  if (indexed_ok_t) {
+    // per-expert scale on device (once per layer/E).
+    struct EscTls {
+      int dev = -1;
+      int64_t E = 0;
+      const void* host_key = nullptr;
+      std::optional<DBuf> sc;
+    };
+    static thread_local EscTls esc_slots[2];
+    EscTls& esc = esc_slots[(compute_dev == 1) ? 1 : 0];
+    float* escale_ptr = nullptr;

.agents/specs/rocm-gemma4-indexed-max-t-donor.md

@@ -0,0 +1,21 @@
+# Donor evidence — #838 indexed-max-T
+
+Pinned **bytes**, not a dirty-tree HEAD. Implementation must copy these slices (or a later
+immutable replacement that research re-reviews), not re-read `/home/don/llms/vllm.cpp`.
+
+Donor includes `kPrefillIndexedNoSyncMaxT` / `DEVICE_GROUP` neighbors. **Those are out of
+scope for this row.** Only `kDecodeIndexedMaxT` (default 63, clamp [1,63]) and the
+`indexed_ok_t` predicate **without** the nosync disjunct are in scope.
+
+| Field | Value |
+|---|---|
+| Donor tree | `/home/don/llms/vllm.cpp` |
+| Donor git HEAD | `2bb4bd8a` (dirty; these slices are **uncommitted** on that tree) |
+| File | `src/vllm/model_executor/models/gemma4_moe.cpp` |
+| Slice A | `rocm-gemma4-indexed-max-t-donor-gate-911-933.log` lines 911–933 SHA256 `d0d28f3d55ff7d526475c9a2a1d028792cc245ba4cc2b421ebf994fed9b96e59` |
+| Slice B | `rocm-gemma4-indexed-max-t-donor-ok-1088-1110.log` lines 1088–1110 SHA256 `5509f3f77dcadd023ce73743e13a2a1a0237d8dd0a8e25a98a765430fc577bd0` |
+| Recipient | `origin/main` `3ce5a1dc` `gemma4_moe.cpp:735` (`T == 1` only) / `:1345` serial |
+| Captured | 2026-08-14 |
+
+`sha256sum` of each slice file must match the table. Do not treat `2bb4bd8a` as a clean
+donor commit.