chore: update changelog for v0.3.13 [skip ci]

Reviewed-on: #89

.bumpversion.toml

@@ -1,5 +1,5 @@
 [tool.bumpversion]
-current_version = "0.3.11"
+current_version = "0.3.13"
 parse = "(?P<major>\\d+)\\.(?P<minor>\\d+)\\.(?P<patch>\\d+)"
 serialize = ["{major}.{minor}.{patch}"]
 search = "{current_version}"

CHANGELOG.md

@@ -1,5 +1,17 @@
 # Changelog
 
+## [0.3.13] - 2026-08-28
+
+### Added
+
+- Add inference-time model_config overrides with a sampling-key allowlist [gitea #87](https://git.larsbogner.de/lars/giant/issues/87)
+
+## [0.3.12] - 2026-08-28
+
+### Added
+
+- Add sampled n_sec under n_sec.mode = 'head' [gitea #86](https://git.larsbogner.de/lars/giant/issues/86)
+
 ## [0.3.11] - 2026-08-26
 
 ### Changed

giant/checkpoint_io.py

@@ -14,11 +14,18 @@ directly and imported from non-CLI code (`giant.analysis.router_gating`,
 lazily — see that module's docstring for why). Failures raise
 `CheckpointCompatibilityError` with the same wording the CLI has always
 shown; the CLI layer catches it and does the `typer.echo`/`Exit(1)`.
+
+`load_for_inference`'s `config_overrides` (gitea #87) lets a caller change a
+checkpoint's `model_config` at load time, restricted to
+`giant.config.INFERENCE_OVERRIDES` — the allowlist of keys that only affect
+sampling, never module construction/shapes or the preprocessing normalizers/
+vocab maps were fit under.
 """
 
 from __future__ import annotations
 
-from dataclasses import dataclass
+import copy
+from dataclasses import dataclass, field
 from pathlib import Path
 
 import torch
@@ -29,13 +36,45 @@ from giant.constants import K_MAX
 from giant.data.loader import TopNMap
 from giant.data.setup_cache import topnmap_from_json
 from giant.data.transforms import Normalizer
-from giant.model.network import build_models
+from giant.model.network import _migrate_legacy_model_config, build_models
 
 
 class CheckpointCompatibilityError(Exception):
     """Checkpoint is missing something `load_for_inference` needs."""
 
 
+def apply_config_overrides(model_cfg: dict, overrides: dict[str, object] | None) -> dict:
+    """Deep-merge dotted-path *overrides* into a checkpoint's `model_config`,
+    validated against `giant.config.INFERENCE_OVERRIDES` — the allowlist of
+    keys that only affect sampling, not module construction/shapes or the
+    preprocessing normalizers/vocab maps were fit under (gitea #87).
+
+    Migrates a v0.2 flat `model_config` to the nested v0.3 shape first: a
+    dotted path like "stage1_model.ddpm.n_steps" would otherwise silently
+    write into a dict that `build_models` still reads as flat (it decides
+    v0.2-vs-v0.3 by `"stage1_model" in model_config`), suppressing migration.
+
+    Raises `CheckpointCompatibilityError` — never a bare `ValueError` or a
+    downstream `load_state_dict` size mismatch — for an unknown/disallowed
+    path or a value that fails its allowlisted check.
+    """
+    if not overrides:
+        return model_cfg
+    cfg = model_cfg if "stage1_model" in model_cfg else _migrate_legacy_model_config(model_cfg)
+    cfg = copy.deepcopy(cfg)
+    for path, value in overrides.items():
+        spec = gconfig.INFERENCE_OVERRIDES.get(path)
+        if spec is None:
+            allowed = ", ".join(sorted(gconfig.INFERENCE_OVERRIDES))
+            raise CheckpointCompatibilityError(f"{path!r} is not an inference-safe override — allowed paths: {allowed}")
+        try:
+            spec.check(path, value)
+        except ValueError as exc:
+            raise CheckpointCompatibilityError(str(exc)) from exc
+        gconfig._set_path(cfg, path, value)
+    return cfg
+
+
 def conditioning_axes(model_cfg: dict, default: str = "embedding") -> tuple[str, str]:
     """(particle_conditioning, material_conditioning) for
     `giant.data.transforms.build_cond_features`/`build_features` — from
@@ -128,6 +167,7 @@ class InferenceContext:
     model_config: dict
     epoch: int | None
     best_val_loss: float | None
+    config_overrides: dict[str, object] = field(default_factory=dict)
 
 
 def load_for_inference(
@@ -136,6 +176,7 @@ def load_for_inference(
     command_name: str,
     weights: str = "raw",
     require_stage2: bool = True,
+    config_overrides: dict[str, object] | None = None,
 ) -> InferenceContext:
     """Load *checkpoint* and reconstruct everything `predict`/`rollout` need
     to run it forward, on *device*, in `eval()` mode.
@@ -148,6 +189,13 @@ def load_for_inference(
     both stages) or an acceptable `stage2 = None` result — kept as a real
     parameter since `stage{1,2}_model.active` is a real, if currently
     stage1+stage2-only-in-practice, config option.
+
+    *config_overrides* deep-merges dotted `model_config` paths (e.g.
+    `{"stage2_model.n_sec.sampling": "sample"}`) before anything is
+    derived from `model_config` or built — see `apply_config_overrides` for
+    the allowlist and validation. Every derived `InferenceContext` field
+    (`other_policy`, `stage{1,2}_ddpm_steps`, the built modules, ...)
+    reflects the overridden config.
     """
     ckpt = torch.load(checkpoint, map_location="cpu", weights_only=False)
     for key in ("model_config", "sec_decoder"):
@@ -159,7 +207,7 @@ def load_for_inference(
 
     gconfig.warn_if_checkpoint_config_mismatch(checkpoint)
 
-    model_cfg = ckpt["model_config"]
+    model_cfg = apply_config_overrides(ckpt["model_config"], config_overrides)
     particle_conditioning, material_conditioning = conditioning_axes(model_cfg)
     pdg_topn_map = load_pdg_topn_map(ckpt)
     mat_topn_map = load_mat_topn_map(ckpt)
@@ -231,4 +279,5 @@ def load_for_inference(
         model_config=model_cfg,
         epoch=ckpt.get("epoch"),
         best_val_loss=ckpt.get("best_val_loss"),
+        config_overrides=dict(config_overrides) if config_overrides else {},
     )

giant/cli.py

@@ -141,6 +141,23 @@ def _parse_router_axis_flags(specs: list[str]) -> dict[str, object]:
     return out
 
 
+def _parse_set_flags(specs: Optional[list[str]]) -> dict[str, object]:
+    """Parse repeated `--set dotted.path=value` flags into a dict, typing
+    each value with `_coerce_scalar` the same way a TOML file's native types
+    would arrive. Validation against the inference-safe allowlist happens
+    downstream in `giant.checkpoint_io.apply_config_overrides` — this only
+    parses syntax.
+    """
+    out: dict[str, object] = {}
+    for spec in specs or []:
+        path, sep, val = spec.partition("=")
+        if not sep:
+            typer.echo(f"error: --set {spec!r} must be 'dotted.path=value'", err=True)
+            raise typer.Exit(1)
+        out[path] = _coerce_scalar(val)
+    return out
+
+
 def _router_cli_overrides(
     router: bool | None,
     router_type: str | None,
@@ -1020,6 +1037,15 @@ def predict(
             help="Free-text note recorded in the prediction's YAML sidecar",
         ),
     ] = None,
+    set_: Annotated[
+        Optional[list[str]],
+        typer.Option(
+            "--set",
+            help="Override a sampling-only model_config key on this checkpoint, "
+            "'dotted.path=value' (repeatable) — see giant.config.INFERENCE_OVERRIDES "
+            "for the allowlist, e.g. --set stage2_model.n_sec.sampling=sample",
+        ),
+    ] = None,
 ) -> None:
     """Run trained model on a parquet file and save predictions."""
     batch_size_auto = False
@@ -1040,8 +1066,11 @@ def predict(
     typer.echo(f"device: {_device}")
 
     # --- Load checkpoint ---
+    config_overrides = _parse_set_flags(set_)
     try:
-        ctx = load_for_inference(checkpoint, _device, "predict", weights=weights.value)
+        ctx = load_for_inference(
+            checkpoint, _device, "predict", weights=weights.value, config_overrides=config_overrides
+        )
     except CheckpointCompatibilityError as exc:
         typer.echo(f"error: {exc}", err=True)
         raise typer.Exit(1)
@@ -1407,6 +1436,15 @@ def rollout(
         Optional[int],
         typer.Option("--seed", help="Torch/numpy seed for reproducibility"),
     ] = None,
+    set_: Annotated[
+        Optional[list[str]],
+        typer.Option(
+            "--set",
+            help="Override a sampling-only model_config key on this checkpoint, "
+            "'dotted.path=value' (repeatable) — see giant.config.INFERENCE_OVERRIDES "
+            "for the allowlist, e.g. --set stage2_model.n_sec.sampling=sample",
+        ),
+    ] = None,
 ) -> None:
     """Roll the surrogate forward into full showers (autoregressive)."""
     if seed is not None:
@@ -1416,8 +1454,11 @@ def rollout(
     _device = torch.device(device) if device else gconfig.auto_device()
     typer.echo(f"device: {_device}")
 
+    config_overrides = _parse_set_flags(set_)
     try:
-        ctx = load_for_inference(checkpoint, _device, "rollout", weights=weights.value)
+        ctx = load_for_inference(
+            checkpoint, _device, "rollout", weights=weights.value, config_overrides=config_overrides
+        )
     except CheckpointCompatibilityError as exc:
         typer.echo(f"error: {exc}", err=True)
         raise typer.Exit(1)
@@ -1532,6 +1573,7 @@ def rollout(
             # model knob (router type/n_experts, noise_dim, vocab sizes, ...)
             # is available downstream without touching this command again.
             "model_config": dict(model_cfg),
+            "config_overrides": dict(ctx.config_overrides),
             "training_epoch": ctx.epoch,
             "best_val_loss": ctx.best_val_loss,
             # [train]/[meta] from the sibling config.toml (giant.config.save_config)

giant/config.py

@@ -404,6 +404,16 @@ class Stage2RouterConfig(RouterConfig):
         return {"tie_to_stage1": self.tie_to_stage1, **super().to_dict()}
 
 
+# stage2_model.n_sec.sampling choices — single source of truth for both
+# validate_config's train-time check and INFERENCE_OVERRIDES below.
+STOP_SAMPLING_CHOICES = ("greedy", "sample")
+
+# stage2_model.particle_type.other_policy choices — see ParticleTypeConfig's
+# docstring for what each means; only documented there until now, since
+# nothing validated it at train time.
+OTHER_POLICY_CHOICES = ("sample", "modal", "drop")
+
+
 @dataclass(frozen=True)
 class NSecConfig:
     # "head": a classifier over {0..k_max} on the condition encoding alone
@@ -424,11 +434,15 @@ class NSecConfig:
     # n_sec head was trained against Stage 1's own ConditionEncoder output and so has
     # to stay attached there, not just be labeled as such).
     owner: str = "stage2"
-    # mode="stop_token" only: how sample_secondaries_ar turns a slot's stop logit into a
+    # How resolve_n_sec/sample_secondaries_ar turn a count-bearing head's output into an
-    # stop/continue decision. "greedy": sigmoid(logit) >= 0.5 (deterministic). "sample":
+    # actual n_sec decision. mode="head": "greedy" is argmax over the classifier logits
-    # a Bernoulli draw at sigmoid(logit) (a real sample from the learned length
+    # (deterministic — the conditional mode, not a sample); "sample" is a categorical draw
-    # distribution, at the cost of an extra RNG draw per slot).
+    # from softmax(logits) (a real sample from the learned count distribution). mode=
-    stop_sampling: str = "greedy"
+    # "stop_token": "greedy" is sigmoid(stop_logit) >= 0.5 per slot (deterministic);
+    # "sample" is a Bernoulli draw at sigmoid(stop_logit) per slot. Renamed from
+    # "stop_sampling" (gitea #86), which is still accepted as a deprecated alias since it
+    # appears in existing checkpoints' model_config.
+    sampling: str = "greedy"
 
     @classmethod
     def from_dict(cls, d: dict | None) -> "NSecConfig":
@@ -437,7 +451,7 @@ class NSecConfig:
             mode=d.get("mode", "head"),
             lambda_weight=d.get("lambda", 0.1),
             owner=d.get("owner", "stage2"),
-            stop_sampling=d.get("stop_sampling", "greedy"),
+            sampling=d.get("sampling", d.get("stop_sampling", "greedy")),
         )
 
     def to_dict(self) -> dict:
@@ -445,7 +459,7 @@ class NSecConfig:
             "mode": self.mode,
             "lambda": self.lambda_weight,
             "owner": self.owner,
-            "stop_sampling": self.stop_sampling,
+            "sampling": self.sampling,
         }
 
 
@@ -1075,6 +1089,27 @@ def _set_path(d: dict, dotted: str, value) -> None:
     cur[parts[-1]] = value
 
 
+def _pop_path(d: dict, dotted: str) -> None:
+    """Remove a dotted path from a nested dict, if present. No-op if any
+    component along the path is missing."""
+    parts = dotted.split(".")
+    cur = d
+    for part in parts[:-1]:
+        if not isinstance(cur, dict) or part not in cur:
+            return
+        cur = cur[part]
+    if isinstance(cur, dict):
+        cur.pop(parts[-1], None)
+
+
+# Config keys renamed within v0.3 itself (not part of the v0.2->v0.3 migration
+# above) — normalized by migrate_config so a config.toml still using an older
+# v0.3 key name keeps passing validate_config_keys.
+_RENAMED_KEYS = {
+    "stage2_model.n_sec.stop_sampling": "stage2_model.n_sec.sampling",  # gitea #86
+}
+
+
 def _deep_merge(base: dict, override: dict) -> dict:
     """Recursively merge `override` onto a copy of `base`.
 
@@ -1093,6 +1128,72 @@ def _deep_merge(base: dict, override: dict) -> dict:
     return result
 
 
+@dataclass(frozen=True)
+class InferenceOverride:
+    """One dotted `model_config` path that `giant.checkpoint_io.load_for_inference`
+    is allowed to change on an already-trained checkpoint, without retraining.
+
+    A path only belongs here if it affects neither module construction/tensor
+    shapes nor the data preprocessing the normalizers/vocab maps were fit
+    under — see the module docstring on `giant.model.summary` for the class
+    of key this targets (`_fingerprint`'s "plain scalar attribute" leaves),
+    and `giant.checkpoint_io.apply_config_overrides` for where this is used.
+    """
+
+    why: str
+    choices: tuple[str, ...] | None = None
+    minimum: float | None = None
+    numeric: bool = False  # int/float leaf (vs. str, the default)
+
+    def check(self, path: str, value: object) -> None:
+        if self.choices is not None:
+            if value not in self.choices:
+                raise ValueError(f"{path} = {value!r} — must be one of {self.choices}")
+            return
+        if self.numeric:
+            if isinstance(value, bool) or not isinstance(value, (int, float)):
+                raise ValueError(f"{path} = {value!r} — must be a number")
+            if self.minimum is not None and value < self.minimum:
+                raise ValueError(f"{path} = {value!r} — must be >= {self.minimum}")
+
+
+# Inference-safe dotted `model_config` paths — the allowlist gitea #87 asked
+# for, so a typo or a shape-bearing key (e.g. "stage1_model.hidden_dim")
+# raises a clear CheckpointCompatibilityError instead of surfacing as an
+# opaque load_state_dict size mismatch later. Extend this table, not a
+# per-call bypass, when a new inference-only key needs the capability.
+INFERENCE_OVERRIDES: dict[str, InferenceOverride] = {
+    "stage2_model.n_sec.sampling": InferenceOverride(
+        why="giant.sample's n_sec head/stop-token sampling reads this at sample time only (gitea #86)",
+        choices=STOP_SAMPLING_CHOICES,
+    ),
+    "stage1_model.ddpm.n_steps": InferenceOverride(
+        why="giant.model.schedule.CosineSchedule's step count, resolved at sample time",
+        numeric=True,
+        minimum=1,
+    ),
+    "stage2_model.ddpm.n_steps": InferenceOverride(
+        why="giant.model.schedule.CosineSchedule's step count, resolved at sample time",
+        numeric=True,
+        minimum=1,
+    ),
+    "stage2_model.particle_type.other_policy": InferenceOverride(
+        why="giant.rollout resolves an 'other'-bucket secondary's PDG code with this at rollout time",
+        choices=OTHER_POLICY_CHOICES,
+    ),
+    "stage1_model.router.temperature": InferenceOverride(
+        why="giant.model.routers.EnergyRouter.temperature, a plain constructor attribute",
+        numeric=True,
+        minimum=1e-6,
+    ),
+    "stage2_model.router.temperature": InferenceOverride(
+        why="giant.model.routers.EnergyRouter.temperature, a plain constructor attribute",
+        numeric=True,
+        minimum=1e-6,
+    ),
+}
+
+
 @dataclass(frozen=True)
 class FlagSpec:
     """One CLI flag's mapping into the config-overrides tree.
@@ -1271,11 +1372,21 @@ def migrate_config(cfg: dict) -> dict:
     (which additionally carries n_sec_head ownership and needs
     `network.build_models`'s cooperation) is a separate migration surface,
     deferred to the network.py refactor.
-    """
-    if _get_path(cfg, "meta.config_version") == CONFIG_VERSION:
-        return copy.deepcopy(cfg)
 
+    Independently of the v0.2/v0.3 branch below, `_RENAMED_KEYS` normalizes
+    keys renamed within v0.3 itself (e.g. `stop_sampling` -> `sampling`,
+    gitea #86) so a config.toml written against an older v0.3 key name still
+    passes `validate_config_keys`.
+    """
     cfg = copy.deepcopy(cfg)
+    for old_path, new_path in _RENAMED_KEYS.items():
+        if _get_path(cfg, old_path) is not None and _get_path(cfg, new_path) is None:
+            _set_path(cfg, new_path, _get_path(cfg, old_path))
+        _pop_path(cfg, old_path)
+
+    if _get_path(cfg, "meta.config_version") == CONFIG_VERSION:
+        return cfg
+
     old_train = cfg.pop("train", {})
     old_model = cfg.pop("model", {})
     old_router = dict(old_model.pop("router", {}))
@@ -1512,9 +1623,9 @@ def validate_config(cfg: dict, *, resume: bool = False) -> None:
                 "conditioning to hang an EOS decision off"
             )
 
-    stop_sampling = _get_path(cfg, "stage2_model.n_sec.stop_sampling")
+    n_sec_sampling = _get_path(cfg, "stage2_model.n_sec.sampling")
-    if stop_sampling not in ("greedy", "sample"):
+    if n_sec_sampling not in STOP_SAMPLING_CHOICES:
-        raise ValueError(f"stage2_model.n_sec.stop_sampling = {stop_sampling!r} — must be 'greedy' or 'sample'")
+        raise ValueError(f"stage2_model.n_sec.sampling = {n_sec_sampling!r} — must be 'greedy' or 'sample'")
 
     precision = _get_path(cfg, "train.precision")
     if precision not in ("fp32", "bf16"):

giant/model/builders.py

@@ -138,7 +138,7 @@ def build_models(model_config: dict) -> dict[str, nn.Module | None]:
                 n_sec_head_cfg=s2_spec.heads.n_sec.to_dict(),
                 type_head_cfg=s2_spec.heads.type.to_dict(),
                 build_stop_head=stop_token,
-                stop_sampling=s2_spec.n_sec.stop_sampling,
+                n_sec_sampling=s2_spec.n_sec.sampling,
                 stop_head_cfg=s2_spec.heads.n_sec.to_dict(),
             )
         else:
@@ -168,6 +168,7 @@ def build_models(model_config: dict) -> dict[str, nn.Module | None]:
                 cond_enc=shared_cond_enc,
                 n_sec_head_cfg=s2_spec.heads.n_sec.to_dict(),
                 type_head_cfg=s2_spec.heads.type.to_dict(),
+                n_sec_sampling=s2_spec.n_sec.sampling,
             )
 
     return result

giant/model/models.py

@@ -370,6 +370,7 @@ class Stage2OneShot(StageModel):
         cond_enc: ConditionEncoder | None = None,
         n_sec_head_cfg: dict | None = None,
         type_head_cfg: dict | None = None,
+        n_sec_sampling: str = "greedy",
     ) -> None:
         super().__init__(
             pdg_vocab,
@@ -383,6 +384,7 @@ class Stage2OneShot(StageModel):
             particle_type_cfg=particle_type_cfg,
             cond_enc=cond_enc,
         )
+        self.n_sec_sampling = n_sec_sampling
         self._build_context_fusion(x_dim, context_dim, cond_out_dim)
         target = self.particle_type_cfg.target
         type_head_out_dim = None if target == "physical" else k_max * self.type_dim
@@ -498,7 +500,7 @@ class Stage2Autoregressive(StageModel):
         n_sec_head_cfg: dict | None = None,
         type_head_cfg: dict | None = None,
         build_stop_head: bool = False,
-        stop_sampling: str = "greedy",
+        n_sec_sampling: str = "greedy",
         stop_head_cfg: dict | None = None,
     ) -> None:
         super().__init__(
@@ -514,7 +516,7 @@ class Stage2Autoregressive(StageModel):
             cond_enc=cond_enc,
         )
         self.history_kind = history
-        self.stop_sampling = stop_sampling
+        self.n_sec_sampling = n_sec_sampling
         self.context_adapter = ContextAdapter(x_dim, context_dim)
         self.base_fuse = nn.Sequential(
             nn.Linear(cond_out_dim + context_dim, cond_out_dim),

giant/model/summary.py

@@ -37,7 +37,7 @@ from dataclasses import dataclass, field
 
 import torch.nn as nn
 
-from giant.config import _get_path, _set_path, leaf_paths
+from giant.config import INFERENCE_OVERRIDES, _get_path, _set_path, leaf_paths
 from giant.model.builders import build_critics, build_models
 from giant.model.trunks import RoutedTrunk
 
@@ -111,6 +111,7 @@ class ModelSummary:
     pdg_vocab: int
     mat_vocab: int
     vocab_caveats: list[str] = field(default_factory=list)
+    overridable: list[str] = field(default_factory=list)
 
 
 def _build_model_config(cfg: dict, pdg_vocab: int, mat_vocab: int) -> dict:
@@ -140,7 +141,7 @@ def _fingerprint(modules: dict[str, nn.Module]) -> list:
     exist, every parameter's/buffer's shape+dtype (never values — those are
     randomly initialized and irrelevant to *structure*), and every plain
     scalar attribute any module stores on itself (e.g. `Stage2Autoregressive
-    .stop_sampling`, `EnergyRouter.temperature`) — this is what makes a
+    .n_sec_sampling`, `EnergyRouter.temperature`) — this is what makes a
     non-parametric key's effect on construction observable."""
     sig = []
     for stage_name, module in modules.items():
@@ -234,6 +235,8 @@ def summarize_model(cfg: dict, pdg_vocab: int, mat_vocab: int) -> ModelSummary:
         else:
             inert.append(path)
 
+    overridable = sorted(p for p in in_scope if p in INFERENCE_OVERRIDES)
+
     return ModelSummary(
         modules=modules,
         consumed=sorted(consumed),
@@ -242,6 +245,7 @@ def summarize_model(cfg: dict, pdg_vocab: int, mat_vocab: int) -> ModelSummary:
         pdg_vocab=pdg_vocab,
         mat_vocab=mat_vocab,
         vocab_caveats=_vocab_caveats(cfg),
+        overridable=overridable,
     )
 
 
@@ -309,6 +313,12 @@ def render_summary(summary: ModelSummary) -> str:
     else:
         lines.append("  (none)")
 
+    if summary.overridable:
+        lines.append("")
+        lines.append("inference-overridable without retraining (giant predict/rollout --set):")
+        for path in summary.overridable:
+            lines.append(f"  {path}  ({INFERENCE_OVERRIDES[path].why})")
+
     if summary.vocab_caveats:
         lines.append("")
         lines.append("vocab placeholder caveats:")

giant/sample.py

@@ -261,7 +261,7 @@ def sample_secondaries_ar(
     slot's own stop logit (`predict_stop`, evaluated on the same prefix
     conditioning as the token itself — see `predict_type`'s docstring for
     why this needs no extra state) decides whether generation should have
-    already stopped, per `sec_decoder.stop_sampling` ("greedy": threshold at
+    already stopped, per `sec_decoder.n_sec_sampling` ("greedy": threshold at
     0; "sample": a Bernoulli draw at `sigmoid(logit)`). A row's own
     `n_sec_pred` is the first slot index where this fires; once every row in
     the batch has fired, the loop breaks before spending a model call on the
@@ -345,7 +345,7 @@ def sample_secondaries_ar(
                 slot_idx,
                 hist=hist,
             ).squeeze(1)
-            if sec_decoder.stop_sampling == "sample":
+            if sec_decoder.n_sec_sampling == "sample":
                 stop_now = torch.rand(B, device=device) < torch.sigmoid(stop_logit)
             else:
                 stop_now = stop_logit >= 0.0
@@ -496,7 +496,12 @@ def resolve_n_sec(
 
     Raises if neither stage owns any n_sec mechanism at all — the only way
     that happens is `stage2_model.n_sec.mode = "truth"`, which is not a valid
-    rollout-/predict-capable checkpoint."""
+    rollout-/predict-capable checkpoint.
+
+    `n_sec.mode = "head"` resolves the classifier logits per
+    `sec_decoder.n_sec_sampling`: "greedy" (default) takes the conditional
+    mode via argmax; "sample" draws a real sample from the learned count
+    distribution via `torch.multinomial` on the softmax — see gitea #86."""
     if n_sec_pred is not None:
         return n_sec_pred
     if getattr(sec_decoder, "stop_head", None) is not None:
@@ -508,4 +513,6 @@ def resolve_n_sec(
             "'truth' is standalone-evaluation-only"
         )
     logits = sec_decoder.predict_n_sec(cond_cont, cond_cat, stage1_out)
+    if sec_decoder.n_sec_sampling == "sample":
+        return torch.multinomial(logits.softmax(dim=-1), 1).squeeze(-1)
     return logits.argmax(dim=-1)

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "giant"
-version = "0.3.11"
+version = "0.3.13"
 description = "Geant4 step-function surrogate via conditional flow matching"
 readme = "README.md"
 requires-python = ">=3.12"

tests/test_checkpoint_io.py

@@ -14,6 +14,7 @@ from giant import config as gconfig
 from giant.checkpoint_io import (
     CheckpointCompatibilityError,
     InferenceContext,
+    apply_config_overrides,
     conditioning_axes,
     load_for_inference,
     stage_cfg,
@@ -278,3 +279,122 @@ def test_stage_cfg_new_shape_returns_subdict():
 def test_stage_cfg_v02_flat_shape_returns_empty_dict():
     model_cfg = {"hidden_dim": 32, "n_blocks": 4}
     assert stage_cfg(model_cfg, "stage2") == {}
+
+
+# ---------------------------------------------------------------------------
+# config_overrides (gitea #87)
+# ---------------------------------------------------------------------------
+
+
+def _router_model_cfg() -> dict:
+    cfg = _model_cfg()
+    cfg["stage1_model"]["router"] = {"enabled": True, "type": "energy", "n_experts": 2}
+    return cfg
+
+
+def test_config_override_n_sec_sampling_changes_stage2_attribute(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    ctx = load_for_inference(
+        checkpoint,
+        torch.device("cpu"),
+        "predict",
+        config_overrides={"stage2_model.n_sec.sampling": "sample"},
+    )
+    assert ctx.stage2 is not None
+    assert ctx.stage2.n_sec_sampling == "sample"
+    assert ctx.config_overrides == {"stage2_model.n_sec.sampling": "sample"}
+
+
+def test_config_override_ddpm_n_steps_changes_context_fields(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    ctx = load_for_inference(
+        checkpoint,
+        torch.device("cpu"),
+        "predict",
+        config_overrides={"stage1_model.ddpm.n_steps": 42, "stage2_model.ddpm.n_steps": 7},
+    )
+    assert ctx.stage1_ddpm_steps == 42
+    assert ctx.stage2_ddpm_steps == 7
+
+
+def test_config_override_other_policy_changes_context_field(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    ctx = load_for_inference(
+        checkpoint,
+        torch.device("cpu"),
+        "predict",
+        config_overrides={"stage2_model.particle_type.other_policy": "modal"},
+    )
+    assert ctx.other_policy == "modal"
+
+
+def test_config_override_router_temperature_changes_router_attribute(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path, model_cfg=_router_model_cfg())
+    ctx = load_for_inference(
+        checkpoint,
+        torch.device("cpu"),
+        "predict",
+        config_overrides={"stage1_model.router.temperature": 1.5},
+    )
+    assert ctx.stage1 is not None
+    assert ctx.stage1.trunk.router.temperature == pytest.approx(1.5)
+
+
+def test_config_override_no_overrides_defaults_to_empty_dict(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    ctx = load_for_inference(checkpoint, torch.device("cpu"), "predict")
+    assert ctx.config_overrides == {}
+
+
+def test_config_override_unknown_path_raises(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    with pytest.raises(CheckpointCompatibilityError, match="not an inference-safe override"):
+        load_for_inference(
+            checkpoint,
+            torch.device("cpu"),
+            "predict",
+            config_overrides={"stage2_model.n_sec.typo": "sample"},
+        )
+
+
+def test_config_override_shape_bearing_key_raises_up_front(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    with pytest.raises(CheckpointCompatibilityError, match="not an inference-safe override"):
+        load_for_inference(
+            checkpoint,
+            torch.device("cpu"),
+            "predict",
+            config_overrides={"stage1_model.hidden_dim": 999},
+        )
+
+
+def test_config_override_bad_value_raises(tmp_path):
+    checkpoint = _write_checkpoint(tmp_path)
+    with pytest.raises(CheckpointCompatibilityError, match="must be one of"):
+        load_for_inference(
+            checkpoint,
+            torch.device("cpu"),
+            "predict",
+            config_overrides={"stage2_model.n_sec.sampling": "maybe"},
+        )
+
+
+def test_apply_config_overrides_no_overrides_returns_same_object():
+    cfg = _model_cfg()
+    assert apply_config_overrides(cfg, None) is cfg
+    assert apply_config_overrides(cfg, {}) is cfg
+
+
+def test_apply_config_overrides_migrates_legacy_flat_model_config_first():
+    legacy_cfg = {
+        "pdg_vocab": len(PDG_MAP),
+        "mat_vocab": len(MAT_MAP),
+        "hidden_dim": 32,
+        "n_blocks": 4,
+        "emb_dim": 8,
+        "dropout": 0.1,
+        "k_max": 5,
+    }
+    merged = apply_config_overrides(legacy_cfg, {"stage1_model.ddpm.n_steps": 10})
+    assert merged["stage1_model"]["ddpm"]["n_steps"] == 10
+    assert merged["stage1_model"]["hidden_dim"] == 32

tests/test_cli_predict.py

@@ -172,3 +172,43 @@ def test_predict_exits_1_on_checkpoint_missing_model_config(tmp_path):
 
     assert result.exit_code == 1
     assert "checkpoint has no model_config" in result.output
+
+
+# ---------------------------------------------------------------------------
+# --set (gitea #87)
+# ---------------------------------------------------------------------------
+
+
+def test_predict_set_flag_without_equals_exits_1(tmp_path):
+    checkpoint = tmp_path / "missing.pt"
+
+    result = runner.invoke(
+        app,
+        ["predict", "dummy.parquet", "--checkpoint", str(checkpoint), "--set", "sampling"],
+    )
+
+    assert result.exit_code == 1
+    assert "must be 'dotted.path=value'" in result.output
+
+
+def test_predict_set_flag_disallowed_path_surfaces_compat_error(tmp_path):
+    checkpoint = tmp_path / "ckpt.pt"
+    torch.save(
+        {"model_config": {"stage1_model": {}, "stage2_model": {}}, "sec_decoder": {}, "normalizer": {"sec_phys": {}}},
+        checkpoint,
+    )
+
+    result = runner.invoke(
+        app,
+        [
+            "predict",
+            "dummy.parquet",
+            "--checkpoint",
+            str(checkpoint),
+            "--set",
+            "stage1_model.hidden_dim=999",
+        ],
+    )
+
+    assert result.exit_code == 1
+    assert "not an inference-safe override" in result.output

tests/test_cli_rollout.py

@@ -31,3 +31,28 @@ def test_rollout_exits_1_on_checkpoint_missing_model_config(tmp_path):
 
     assert result.exit_code == 1
     assert "checkpoint has no model_config" in result.output
+
+
+def test_rollout_set_flag_disallowed_path_surfaces_compat_error(tmp_path):
+    checkpoint = tmp_path / "ckpt.pt"
+    torch.save(
+        {"model_config": {"stage1_model": {}, "stage2_model": {}}, "sec_decoder": {}, "normalizer": {"sec_phys": {}}},
+        checkpoint,
+    )
+
+    result = runner.invoke(
+        app,
+        [
+            "rollout",
+            "dummy.parquet",
+            "--checkpoint",
+            str(checkpoint),
+            "--geometry",
+            "dummy_geometry.pkl",
+            "--set",
+            "stage2_model.n_sec.typo=sample",
+        ],
+    )
+
+    assert result.exit_code == 1
+    assert "not an inference-safe override" in result.output

tests/test_config.py

@@ -171,17 +171,40 @@ def test_n_sec_config_owner_defaults_to_stage2():
 def test_n_sec_config_owner_round_trips():
     n_sec = gconfig.NSecConfig.from_dict({"mode": "head", "owner": "stage1"})
     assert n_sec.owner == "stage1"
-    assert n_sec.to_dict() == {"mode": "head", "lambda": 0.1, "owner": "stage1", "stop_sampling": "greedy"}
+    assert n_sec.to_dict() == {"mode": "head", "lambda": 0.1, "owner": "stage1", "sampling": "greedy"}
 
 
-def test_n_sec_config_stop_sampling_defaults_to_greedy():
+def test_n_sec_config_sampling_defaults_to_greedy():
-    assert gconfig.NSecConfig().stop_sampling == "greedy"
+    assert gconfig.NSecConfig().sampling == "greedy"
 
 
-def test_n_sec_config_stop_sampling_round_trips():
+def test_n_sec_config_sampling_round_trips():
+    n_sec = gconfig.NSecConfig.from_dict({"mode": "stop_token", "sampling": "sample"})
+    assert n_sec.sampling == "sample"
+    assert n_sec.to_dict()["sampling"] == "sample"
+
+
+def test_n_sec_config_stop_sampling_alias_still_honored():
+    """gitea #86: stop_sampling was renamed to sampling; old checkpoints'
+    model_config still carries the old key and must keep working."""
     n_sec = gconfig.NSecConfig.from_dict({"mode": "stop_token", "stop_sampling": "sample"})
-    assert n_sec.stop_sampling == "sample"
+    assert n_sec.sampling == "sample"
-    assert n_sec.to_dict()["stop_sampling"] == "sample"
+    assert "stop_sampling" not in n_sec.to_dict()
+
+
+def test_n_sec_config_sampling_key_wins_over_stop_sampling_alias():
+    n_sec = gconfig.NSecConfig.from_dict({"sampling": "sample", "stop_sampling": "greedy"})
+    assert n_sec.sampling == "sample"
+
+
+def test_migrate_config_renames_stop_sampling_key():
+    cfg = {
+        "meta": {"config_version": gconfig.CONFIG_VERSION},
+        "stage2_model": {"n_sec": {"stop_sampling": "sample"}},
+    }
+    migrated = gconfig.migrate_config(cfg)
+    assert gconfig._get_path(migrated, "stage2_model.n_sec.sampling") == "sample"
+    assert gconfig._get_path(migrated, "stage2_model.n_sec.stop_sampling") is None
 
 
 # ---------------------------------------------------------------------------
@@ -851,13 +874,13 @@ def test_validate_config_stop_token_rejected_for_stage1_owner():
         assert "stop_token" in str(e) and "owner" in str(e)
 
 
-def test_validate_config_bad_stop_sampling_rejected():
+def test_validate_config_bad_n_sec_sampling_rejected():
-    cfg = _cfg_with(**{"stage2_model.n_sec.stop_sampling": "bogus"})
+    cfg = _cfg_with(**{"stage2_model.n_sec.sampling": "bogus"})
     try:
         gconfig.validate_config(cfg)
         assert False, "expected ValueError"
     except ValueError as e:
-        assert "stop_sampling" in str(e)
+        assert "sampling" in str(e)
 
 
 def test_validate_config_default_precision_is_fp32():

tests/test_model_summary.py

@@ -12,6 +12,8 @@ from giant.cli import app
 from giant.materials import MATERIAL_PROPERTIES
 from giant.model.summary import _NOT_BUILD_TIME, _built_modules, _vocab_caveats, summarize_model
 
+INFERENCE_OVERRIDES = gconfig.INFERENCE_OVERRIDES
+
 runner = CliRunner()
 
 _PDG_VOCAB = 300
@@ -53,6 +55,16 @@ def test_not_build_time_allow_list_has_no_stale_entries():
     assert not stale, f"_NOT_BUILD_TIME entries no longer in DEFAULT_CONFIG: {sorted(stale)}"
 
 
+def test_inference_overrides_allow_list_has_no_stale_entries():
+    in_scope = set(gconfig.leaf_paths(gconfig.DEFAULT_CONFIG))
+    stale = set(INFERENCE_OVERRIDES) - in_scope
+    assert not stale, f"INFERENCE_OVERRIDES entries no longer in DEFAULT_CONFIG: {sorted(stale)}"
+
+
+def test_default_config_overridable_lists_every_allowlisted_path(default_summary):
+    assert set(default_summary.overridable) == set(INFERENCE_OVERRIDES)
+
+
 def test_router_disabled_by_default_so_its_fields_are_inert(default_summary):
     assert "stage1_model.router.n_experts" in default_summary.inert
     assert "stage1_model.router.temperature" in default_summary.inert
@@ -135,3 +147,5 @@ def test_cli_default_smoke():
     assert "parameters" in result.output
     assert "trunk" in result.output
     assert "inert under this config" in result.output
+    assert "inference-overridable without retraining" in result.output
+    assert "stage2_model.n_sec.sampling" in result.output

tests/test_sample.py

@@ -14,6 +14,7 @@ from giant.model.network import (
     stage2_trunk_sec_dim,
 )
 from giant.sample import (
+    resolve_n_sec,
     sample_flow,
     sample_secondaries,
     sample_secondaries_ar,
@@ -72,6 +73,7 @@ def _stage2_ar(
     mat: int = 2,
     k_max: int = 5,
     history: str = "markov",
+    n_sec_sampling: str = "greedy",
 ) -> Stage2Autoregressive:
     particle_cfg, material_cfg = _particle_material_cfg(_conditioning_for(target), emb_dim)
     return Stage2Autoregressive(
@@ -89,6 +91,7 @@ def _stage2_ar(
         history=history,
         attn_n_heads=2,
         attn_n_layers=1,
+        n_sec_sampling=n_sec_sampling,
     ).eval()
 
 
@@ -99,7 +102,7 @@ def _expected_type_dim(target: str, emb_dim: int) -> int:
 def _stage2_ar_stop_token(
     target: str,
     generator: str,
-    stop_sampling: str = "greedy",
+    n_sec_sampling: str = "greedy",
     emb_dim: int = 6,
     pdg: int = 3,
     mat: int = 2,
@@ -120,7 +123,7 @@ def _stage2_ar_stop_token(
         particle_type_cfg=ParticleTypeConfig(target=target),
         build_n_sec_head=False,
         build_stop_head=True,
-        stop_sampling=stop_sampling,
+        n_sec_sampling=n_sec_sampling,
     ).eval()
 
 
@@ -267,14 +270,14 @@ def test_sample_secondaries_ar_first_slot_has_no_history():
 # ── Stage2Autoregressive: n_sec.mode = "stop_token" ─────────────────────────
 
 
-@pytest.mark.parametrize("stop_sampling", ["greedy", "sample"])
+@pytest.mark.parametrize("n_sec_sampling", ["greedy", "sample"])
-def test_sample_secondaries_ar_stop_token_forced_stop_gives_zero_secondaries(stop_sampling):
+def test_sample_secondaries_ar_stop_token_forced_stop_gives_zero_secondaries(n_sec_sampling):
     """A stop_head pinned to a large positive logit fires at slot 0 for
     every row under both policies (greedy: sigmoid(logit) >= 0.5; sample:
     a Bernoulli draw at sigmoid(logit) ~= 1) — the loop should break before
     generating any token."""
     B, k_max = 4, 5
-    decoder = _stage2_ar_stop_token("physical", "flow", stop_sampling=stop_sampling, k_max=k_max)
+    decoder = _stage2_ar_stop_token("physical", "flow", n_sec_sampling=n_sec_sampling, k_max=k_max)
     _force_stop_head_logit(decoder, 50.0)
     cond_cont, cond_cat = _cond(B)
     stage1_out = torch.randn(B, X_DIM)
@@ -283,13 +286,13 @@ def test_sample_secondaries_ar_stop_token_forced_stop_gives_zero_secondaries(sto
     assert not sec_valid.any()
 
 
-@pytest.mark.parametrize("stop_sampling", ["greedy", "sample"])
+@pytest.mark.parametrize("n_sec_sampling", ["greedy", "sample"])
-def test_sample_secondaries_ar_stop_token_forced_never_stop_runs_to_k_max(stop_sampling):
+def test_sample_secondaries_ar_stop_token_forced_never_stop_runs_to_k_max(n_sec_sampling):
     """A stop_head pinned to a large negative logit never fires under either
     policy, so every row is capped at k_max (the safety cap, not a modeling
     ceiling)."""
     B, k_max = 4, 5
-    decoder = _stage2_ar_stop_token("physical", "flow", stop_sampling=stop_sampling, k_max=k_max)
+    decoder = _stage2_ar_stop_token("physical", "flow", n_sec_sampling=n_sec_sampling, k_max=k_max)
     _force_stop_head_logit(decoder, -50.0)
     cond_cont, cond_cat = _cond(B)
     stage1_out = torch.randn(B, X_DIM)
@@ -336,3 +339,60 @@ def test_sample_secondaries_ar_none_n_sec_pred_without_stop_head_raises():
     stage1_out = torch.randn(3, X_DIM)
     with pytest.raises(AssertionError):
         sample_secondaries_ar(decoder, cond_cont, cond_cat, stage1_out, None, steps=2)
+
+
+# ── resolve_n_sec: n_sec.mode = "head" sampling policy (gitea #86) ──────────
+
+
+def _force_n_sec_head_bias(decoder: Stage2Autoregressive, bias: torch.Tensor) -> None:
+    """Zeroes n_sec_head's weights and pins its bias, so predict_n_sec
+    returns `bias` (broadcast over the batch) as logits regardless of
+    conditioning — mirrors `_force_stop_head_logit`."""
+    assert decoder.n_sec_head is not None
+    last_linear = decoder.n_sec_head[-1]
+    with torch.no_grad():
+        last_linear.weight.zero_()
+        last_linear.bias.copy_(bias)
+
+
+@pytest.mark.parametrize("n_sec_sampling", ["greedy", "sample"])
+def test_resolve_n_sec_head_mode_sharply_peaked_logits_pick_dominant_class(n_sec_sampling):
+    """A logit vector overwhelmingly favoring one class gives the same
+    answer under both policies — greedy because it's the argmax, sample
+    because softmax puts ~all mass on it."""
+    B, k_max = 8, 5
+    decoder = _stage2_ar("physical", "flow", k_max=k_max, n_sec_sampling=n_sec_sampling)
+    bias = torch.full((k_max + 1,), -50.0)
+    bias[2] = 50.0
+    _force_n_sec_head_bias(decoder, bias)
+    cond_cont, cond_cat = _cond(B)
+    stage1_out = torch.randn(B, X_DIM)
+    n_sec = resolve_n_sec(decoder, decoder, cond_cont, cond_cat, stage1_out, None)
+    assert n_sec is not None
+    assert torch.equal(n_sec, torch.full((B,), 2, dtype=torch.long))
+
+
+def test_resolve_n_sec_head_mode_greedy_is_deterministic_under_flat_logits():
+    B, k_max = 32, 5
+    decoder = _stage2_ar("physical", "flow", k_max=k_max, n_sec_sampling="greedy")
+    _force_n_sec_head_bias(decoder, torch.zeros(k_max + 1))
+    cond_cont, cond_cat = _cond(B)
+    stage1_out = torch.randn(B, X_DIM)
+    n_sec = resolve_n_sec(decoder, decoder, cond_cont, cond_cat, stage1_out, None)
+    assert n_sec is not None
+    assert n_sec.unique().numel() == 1
+
+
+def test_resolve_n_sec_head_mode_sample_varies_under_flat_logits():
+    """Under a flat logit vector, a categorical draw across a large batch
+    should hit more than one class — the whole point of gitea #86: greedy
+    always collapses to one, sample should not."""
+    torch.manual_seed(0)
+    B, k_max = 256, 5
+    decoder = _stage2_ar("physical", "flow", k_max=k_max, n_sec_sampling="sample")
+    _force_n_sec_head_bias(decoder, torch.zeros(k_max + 1))
+    cond_cont, cond_cat = _cond(B)
+    stage1_out = torch.randn(B, X_DIM)
+    n_sec = resolve_n_sec(decoder, decoder, cond_cont, cond_cat, stage1_out, None)
+    assert n_sec is not None
+    assert n_sec.unique().numel() > 1

uv.lock

@@ -675,7 +675,7 @@ wheels = [
 
 [[package]]
 name = "giant"
-version = "0.3.11"
+version = "0.3.13"
 source = { editable = "." }
 dependencies = [
     { name = "numpy" },