fix(providers): effort snapping is ordinal — round up, cap at the ceiling

The knob domain grew xhigh/max after the snapping fallbacks were
written, which silently inverted their semantics: off-list meant
"unrecognized string" then, but now usually means "above the model's
ceiling", where falling back to the default tier is directionally
wrong (grok-4.3 at knob max got low; values low/medium/high at knob
xhigh got medium; Anthropic manual mode gave xhigh/max a 4096 budget
while high got 16384).

One rule everywhere now, via snap_reasoning_effort in _protocol:
exact match wins; otherwise the smallest declared level ranking at or
above the knob; above the ceiling, the ceiling. "none" is never a
snap target, and default_reasoning_effort only catches values the
ordinal snap cannot rank.

- resolve_reasoning_effort (flat chat / responses / validated
  effort_param lanes) snaps ordinally: xhigh over (low, medium, high)
  now sends high; xhigh over DeepSeek-style (high, max) sends max —
  matching DeepSeek's official xhigh-to-max aliasing, so a declared
  values list now reproduces that contract instead of defeating it.
- _map_reasoning_to_effort (native output_config) rounds up too:
  knob xhigh on Opus 4.6 (low, medium, high, max) rides max instead
  of silently dropping output_config.
- EFFORT_BUDGET_MAP is monotone across the whole knob domain:
  minimal/low 1024 (API floor), medium 4096, high 16384, xhigh 32768,
  max 65536. Unknown strings still fall to the 4096 default.

Google defaults are unaffected (ceiling and default coincide at
high); wire goldens unchanged. Parity harness caught the budget
clamp interacting with its own max_tokens during development —
capture budget raised above the largest manual budget.

docs/architecture.md

@@ -820,13 +820,19 @@ the levers live in the chat template, reached through
   `effort_param` (e.g. `"reasoning_effort"`), plus optional
   `reasoning_effort_values` / `default_reasoning_effort` to validate
   the knob before it reaches the template; without declared values the
-  knob is forwarded as-is. Only declare values that match the
-  template's documented vocabulary — snapping an off-list knob to the
-  default can defeat a real tier. DeepSeek-V4, for example, officially
+  knob is forwarded as-is. The knob is ordinal, and validation
+  respects that: an off-list knob value rounds UP onto the declared
+  list and a value above the ceiling rides the ceiling
+  (`snap_reasoning_effort`) — asking for more effort than the model
+  declares never falls back to a lower default tier.
+  `default_reasoning_effort` only catches values the ordinal snap
+  cannot rank (custom strings). Declare values that match the
+  template's documented vocabulary: for DeepSeek-V4, which officially
   accepts `high`/`max` (Think High is the default thinking tier;
-  `low`/`medium` alias to `high`, `xhigh` to `max`), so freeform
-  passthrough matches the contract while a `("low", "medium", "high")`
-  values list would make Think Max unreachable. To map an undocumented
+  `low`/`medium` alias to `high`, `xhigh` to `max`), a
+  `("high", "max")` values list reproduces the official aliasing
+  exactly — `low`/`medium` round up to `high`, `xhigh` to `max` —
+  and freeform passthrough matches it too. To map an undocumented
   template, probe with per-request `chat_template_kwargs` and compare
   `input_tokens`. Setting `effort_param` also suppresses the
   flat top-level `reasoning_effort` request param on the