diff --git a/benchmarks/measurements/2026-09-08-module-audit.json b/benchmarks/measurements/2026-09-08-module-audit.json
index b466258..1c995e4 100644
--- a/benchmarks/measurements/2026-09-08-module-audit.json
+++ b/benchmarks/measurements/2026-09-08-module-audit.json
@@ -1,7 +1,7 @@
 {
-  "modules": 118,
+  "modules": 120,
   "counts": {
-    "load_bearing": 109,
+    "load_bearing": 111,
     "standalone_capability": 9
   },
   "orphaned": [],
@@ -400,6 +400,7 @@
         "model.scan",
         "model.specs",
         "model.taint",
+        "plane.budget",
         "preprocess",
         "push.assistance",
         "push.cache",
@@ -409,7 +410,8 @@
         "push.reuse",
         "push.runner",
         "push.snapshot",
-        "push.vetoes"
+        "push.vetoes",
+        "tool_hunter"
       ]
     },
     {
@@ -479,7 +481,9 @@
       "reason": "model-grounded-detection Req 8: the judge client, wired by model/judge.py in group 3",
       "importers": [
         "cli",
-        "push.assistance"
+        "plane.budget",
+        "push.assistance",
+        "tool_hunter"
       ]
     },
     {
@@ -645,6 +649,18 @@
         "pair_gate"
       ]
     },
+    {
+      "module": "plane",
+      "classification": "load_bearing",
+      "reason": "ai-service-plane Req 1-4: the service plane package; runner and reconciler integration in tasks 3-4",
+      "importers": []
+    },
+    {
+      "module": "plane.budget",
+      "classification": "load_bearing",
+      "reason": "ai-service-plane Req 2.3/2.4: metered chat client with usd and calls ceilings; task integration in tasks 3, 6",
+      "importers": []
+    },
     {
       "module": "policy",
       "classification": "load_bearing",
@@ -1041,6 +1057,7 @@
         "mapping",
         "model.candidates",
         "model.layout",
+        "model.scan",
         "model.specs",
         "pairs",
         "semantic.cst",
@@ -1048,6 +1065,7 @@
         "semantic.functions",
         "semantic.ir",
         "semantic.obligations.check",
+        "semantic.obligations.facts",
         "semantic.obligations.operations",
         "semantic.obligations.shapes",
         "semantic.overlay",
@@ -1093,10 +1111,12 @@
         "mapping",
         "model.candidates",
         "model.layout",
+        "model.scan",
         "model.specs",
         "pairs",
         "semantic",
         "semantic.obligations.check",
+        "semantic.obligations.facts",
         "semantic.obligations.operations",
         "semantic.obligations.shapes",
         "semantic.overlay",
@@ -1293,7 +1313,8 @@
       "classification": "load_bearing",
       "reason": "reachable from gate, map_gate, pair_gate or the CLI",
       "importers": [
-        "model.endpoint"
+        "model.endpoint",
+        "plane.budget"
       ]
     },
     {
diff --git a/src/openultrasast/model/audit.py b/src/openultrasast/model/audit.py
index 7544f0e..99132c1 100644
--- a/src/openultrasast/model/audit.py
+++ b/src/openultrasast/model/audit.py
@@ -54,6 +54,8 @@ SPEC_OWNED = {
     "cpg": "model-grounded-detection Req 4: the CPG seam package",
     "cpg.backend": "model-grounded-detection Req 4.1/4.5: the single Joern subprocess boundary",
     "cpg.capability": "model-grounded-detection Req 4.2/4.3: the engine probe that degrades to suspicion",
+    "plane": "ai-service-plane Req 1-4: the service plane package; runner and reconciler integration in tasks 3-4",
+    "plane.budget": "ai-service-plane Req 2.3/2.4: metered chat client with usd and calls ceilings; task integration in tasks 3, 6",
 }
 
 STANDALONE = {
diff --git a/src/openultrasast/plane/__init__.py b/src/openultrasast/plane/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/openultrasast/plane/budget.py b/src/openultrasast/plane/budget.py
new file mode 100644
index 0000000..7db2e68
--- /dev/null
+++ b/src/openultrasast/plane/budget.py
@@ -0,0 +1,163 @@
+"""Budget metering for a task's model calls (ai-service-plane, Requirement 2.3 / 2.4).
+
+`MeteredClient` wraps any `ChatClient`, sums the provider's usage fields per call, prices them from a Model
+manifest's parameters, and stops the task at its ceiling. Two failure shapes are distinct on purpose: a ceiling
+is `BudgetExhausted` (the task is `unfinished` and resumes under a larger budget), an account or authentication
+failure is `AccountError` (the task is `failed` and the run starts nothing further). A model without prices is
+`unpriced`, which is not zero dollars: such a client refuses a usd budget rather than reporting a clean 0.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Mapping
+from typing import Any
+
+from ..model.endpoint import Prices
+from ..tool_hunter import ChatClient, ChatResponse
+
+_ACCOUNT_MARKERS = ("HTTP Error 401", "HTTP Error 402", "Insufficient Balance")
+_USAGE_FIELDS = ("prompt_tokens", "prompt_cache_hit_tokens", "completion_tokens")
+
+
+class BudgetExhausted(RuntimeError):
+    """Raised before a call would start once the usd or calls ceiling is reached."""
+
+    def __init__(self, message: str, *, usd: float | None, calls: int) -> None:
+        super().__init__(message)
+        self.usd = usd
+        self.calls = calls
+
+
+class AccountError(RuntimeError):
+    """Raised when the provider refuses the account: 401, 402 or an insufficient-balance body."""
+
+    def __init__(self, provider_message: str) -> None:
+        super().__init__(provider_message)
+        self.provider_message = provider_message
+
+
+def is_account_error(exc: BaseException) -> bool:
+    text = str(exc).lower()
+    return any(marker.lower() in text for marker in _ACCOUNT_MARKERS)
+
+
+def prices_from(parameters: Mapping[str, object] | Prices | None) -> Prices | None:
+    """Prices from a Model manifest's `spec.parameters` (or an existing `Prices`); None when any rate is missing."""
+    if parameters is None or isinstance(parameters, Prices):
+        return parameters
+    values: list[float] = []
+    for key in ("cache_hit_per_m", "input_per_m", "output_per_m"):
+        value = parameters.get(key)
+        if not isinstance(value, int | float) or isinstance(value, bool):
+            return None
+        values.append(float(value))
+    return Prices(cache_hit_per_m=values[0], input_per_m=values[1], output_per_m=values[2])
+
+
+def cost_of(usage: Mapping[str, object], prices: Prices) -> float:
+    """Dollars for one call from the provider's usage fields, the arithmetic of `ChatEndpoint.cost`."""
+    cache_hit = _tokens(usage.get("prompt_cache_hit_tokens"))
+    miss = usage.get("prompt_cache_miss_tokens")
+    input_tokens = _tokens(miss) if miss is not None else max(_tokens(usage.get("prompt_tokens")) - cache_hit, 0)
+    output_tokens = _tokens(usage.get("completion_tokens"))
+    return (cache_hit * prices.cache_hit_per_m + input_tokens * prices.input_per_m + output_tokens * prices.output_per_m) / 1_000_000
+
+
+class MeteredClient:
+    """A `ChatClient` that meters spend from the wrapped client's provider usage rows.
+
+    The wrapped client is expected to record one usage dict per call in a `usage` list (as `DeepSeekChatClient`
+    does); rows appended during a call are attributed to it. A client without that list still has its calls
+    counted, with zero tokens.
+    """
+
+    def __init__(
+        self,
+        inner: ChatClient,
+        *,
+        prices: Mapping[str, object] | Prices | None = None,
+        budget_usd: float | None = None,
+        budget_calls: int | None = None,
+    ) -> None:
+        self.inner = inner
+        self.prices = prices_from(prices)
+        if budget_usd is not None and self.prices is None:
+            raise ValueError("unpriced model cannot run under a usd budget")
+        if budget_usd is not None and budget_usd < 0:
+            raise ValueError("budget_usd must not be negative")
+        if budget_calls is not None and budget_calls < 0:
+            raise ValueError("budget_calls must not be negative")
+        self.budget_usd = budget_usd
+        self.budget_calls = budget_calls
+        self.calls = 0
+        self.usage: dict[str, int] = dict.fromkeys(_USAGE_FIELDS, 0)
+        self._usd = 0.0
+        self._seen_rows = len(self._inner_rows())
+
+    @property
+    def priced(self) -> bool:
+        return self.prices is not None
+
+    @property
+    def usd(self) -> float | None:
+        return self._usd if self.prices is not None else None
+
+    def check(self) -> None:
+        """Raise `BudgetExhausted` when the next call must not start."""
+        if self.budget_usd is not None and self._usd >= self.budget_usd:
+            raise BudgetExhausted(
+                f"usd budget exhausted: spent {self._usd:.6f} of {self.budget_usd:.6f} after {self.calls} calls",
+                usd=self._usd,
+                calls=self.calls,
+            )
+        if self.budget_calls is not None and self.calls >= self.budget_calls:
+            raise BudgetExhausted(f"calls budget exhausted: {self.calls} of {self.budget_calls}", usd=self.usd, calls=self.calls)
+
+    def complete(
+        self,
+        *,
+        model: str,
+        messages: list[dict[str, object]],
+        tools: list[dict[str, object]],
+        timeout_seconds: int = 60,
+        json_object: bool = False,
+    ) -> ChatResponse:
+        self.check()
+        try:
+            response = self.inner.complete(
+                model=model, messages=messages, tools=tools, timeout_seconds=timeout_seconds, json_object=json_object
+            )
+        except Exception as exc:
+            self._absorb_rows()
+            if is_account_error(exc):
+                raise AccountError(str(exc)) from exc
+            raise
+        self.calls += 1
+        self._absorb_rows()
+        return response
+
+    def summary(self) -> dict[str, Any]:
+        """The spend block of a task's `summary.json`: `usd` is None, not 0, for an unpriced model."""
+        return {"usd": self.usd, "calls": self.calls, "usage": dict(self.usage), "priced": self.priced}
+
+    def _inner_rows(self) -> list[Any]:
+        rows = getattr(self.inner, "usage", None)
+        return rows if isinstance(rows, list) else []
+
+    def _absorb_rows(self) -> None:
+        rows = self._inner_rows()
+        for row in rows[self._seen_rows :]:
+            if not isinstance(row, Mapping):
+                continue
+            for field in _USAGE_FIELDS:
+                self.usage[field] += _tokens(row.get(field))
+            if self.prices is not None:
+                self._usd += cost_of(row, self.prices)
+        self._seen_rows = len(rows)
+
+
+def _tokens(value: object) -> int:
+    return int(value) if isinstance(value, int | float) and not isinstance(value, bool) else 0
+
+
+__all__ = ["AccountError", "BudgetExhausted", "MeteredClient", "cost_of", "is_account_error", "prices_from"]
diff --git a/tests/test_plane_budget.py b/tests/test_plane_budget.py
new file mode 100644
index 0000000..266e600
--- /dev/null
+++ b/tests/test_plane_budget.py
@@ -0,0 +1,193 @@
+"""Budget metering (ai-service-plane task 2): ceilings, account errors, unpriced refusal, cache-hit pricing."""
+
+from __future__ import annotations
+
+import pytest
+
+from openultrasast.model.endpoint import Prices
+from openultrasast.plane.budget import AccountError, BudgetExhausted, MeteredClient, cost_of, prices_from
+from openultrasast.tool_hunter import ChatResponse
+
+FLASH = {"cache_hit_per_m": 0.014, "input_per_m": 0.44, "output_per_m": 1.32}
+MESSAGES: list[dict[str, object]] = [{"role": "user", "content": "hi"}]
+
+
+class UsageClient:
+    """Records provider usage rows like DeepSeekChatClient; a scripted step may raise instead."""
+
+    def __init__(self, steps: list[dict[str, object] | Exception]) -> None:
+        self.steps = list(steps)
+        self.usage: list[dict[str, object]] = []
+        self.calls = 0
+
+    def complete(
+        self,
+        *,
+        model: str,
+        messages: list[dict[str, object]],
+        tools: list[dict[str, object]],
+        timeout_seconds: int = 60,
+        json_object: bool = False,
+    ) -> ChatResponse:
+        self.calls += 1
+        step = self.steps.pop(0)
+        if isinstance(step, Exception):
+            raise step
+        self.usage.append(dict(step))
+        return ChatResponse(content="ok")
+
+
+def _row(prompt: int, cache_hit: int, completion: int) -> dict[str, object]:
+    return {"prompt_tokens": prompt, "prompt_cache_hit_tokens": cache_hit, "completion_tokens": completion}
+
+
+def _call(client: MeteredClient) -> ChatResponse:
+    return client.complete(model="m", messages=MESSAGES, tools=[])
+
+
+def test_cache_hit_pricing_is_exact_dollars() -> None:
+    # 1_000_000 prompt tokens of which 250_000 hit the cache, 100_000 completion tokens:
+    # 250_000 * 0.014/M + 750_000 * 0.44/M + 100_000 * 1.32/M = 0.0035 + 0.33 + 0.132
+    inner = UsageClient([_row(1_000_000, 250_000, 100_000)])
+    metered = MeteredClient(inner, prices=FLASH)
+    _call(metered)
+    assert metered.usd == pytest.approx(0.4655, abs=1e-12)
+    assert metered.calls == 1
+    assert metered.usage == {"prompt_tokens": 1_000_000, "prompt_cache_hit_tokens": 250_000, "completion_tokens": 100_000}
+
+
+def test_cost_of_honours_explicit_cache_miss_field() -> None:
+    prices = Prices(cache_hit_per_m=1.0, input_per_m=10.0, output_per_m=100.0)
+    row = {"prompt_tokens": 30, "prompt_cache_hit_tokens": 10, "prompt_cache_miss_tokens": 20, "completion_tokens": 5}
+    assert cost_of(row, prices) == pytest.approx((10 * 1.0 + 20 * 10.0 + 5 * 100.0) / 1_000_000)
+
+
+def test_usage_sums_across_calls() -> None:
+    inner = UsageClient([_row(100, 40, 10), _row(200, 0, 20)])
+    metered = MeteredClient(inner, prices=FLASH)
+    _call(metered)
+    _call(metered)
+    assert metered.usage == {"prompt_tokens": 300, "prompt_cache_hit_tokens": 40, "completion_tokens": 30}
+    expected = (40 * 0.014 + 60 * 0.44 + 10 * 1.32 + 200 * 0.44 + 20 * 1.32) / 1_000_000
+    assert metered.usd == pytest.approx(expected)
+
+
+def test_usd_ceiling_stops_before_the_next_call() -> None:
+    # each call costs exactly 1.32 usd (1M completion tokens); the budget of 2.0 admits two calls, not three
+    inner = UsageClient([_row(0, 0, 1_000_000)] * 3)
+    metered = MeteredClient(inner, prices=FLASH, budget_usd=2.0)
+    _call(metered)
+    _call(metered)
+    with pytest.raises(BudgetExhausted) as info:
+        _call(metered)
+    assert inner.calls == 2, "the third call must not reach the provider"
+    assert info.value.calls == 2
+    assert info.value.usd == pytest.approx(2.64)
+    assert isinstance(info.value, RuntimeError)
+
+
+def test_calls_ceiling_stops_before_the_next_call() -> None:
+    inner = UsageClient([_row(1, 0, 1)] * 3)
+    metered = MeteredClient(inner, prices=FLASH, budget_calls=2)
+    _call(metered)
+    _call(metered)
+    with pytest.raises(BudgetExhausted) as info:
+        _call(metered)
+    assert inner.calls == 2
+    assert info.value.calls == 2
+
+
+def test_zero_calls_budget_refuses_the_first_call() -> None:
+    inner = UsageClient([_row(1, 0, 1)])
+    metered = MeteredClient(inner, budget_calls=0)
+    with pytest.raises(BudgetExhausted):
+        _call(metered)
+    assert inner.calls == 0
+
+
+@pytest.mark.parametrize(
+    "message",
+    [
+        'OpenRouter chat request failed: HTTPError: HTTP Error 402: Payment Required: {"error":{"message":"Insufficient credits"}}',
+        "OpenRouter chat request failed: HTTPError: HTTP Error 401: Unauthorized",
+        'DeepSeek chat request failed: {"error":{"message":"Insufficient Balance","type":"unknown_error"}}',
+    ],
+)
+def test_account_errors_are_distinct_and_carry_the_provider_message(message: str) -> None:
+    inner = UsageClient([RuntimeError(message)])
+    metered = MeteredClient(inner, prices=FLASH, budget_usd=5.0)
+    with pytest.raises(AccountError) as info:
+        _call(metered)
+    assert info.value.provider_message == message
+    assert isinstance(info.value.__cause__, RuntimeError)
+    assert metered.calls == 0
+
+
+def test_other_provider_errors_pass_through_unchanged() -> None:
+    inner = UsageClient([RuntimeError("OpenRouter chat request failed: HTTPError: HTTP Error 503: Service Unavailable")])
+    metered = MeteredClient(inner, prices=FLASH)
+    with pytest.raises(RuntimeError, match="503") as info:
+        _call(metered)
+    assert not isinstance(info.value, AccountError)
+
+
+def test_unpriced_model_refuses_a_usd_budget() -> None:
+    with pytest.raises(ValueError, match="unpriced model cannot run under a usd budget"):
+        MeteredClient(UsageClient([]), budget_usd=1.0)
+    with pytest.raises(ValueError, match="unpriced"):
+        MeteredClient(UsageClient([]), prices={"input_per_m": 0.44}, budget_usd=1.0)
+
+
+def test_unpriced_model_reports_none_not_zero_under_a_calls_budget() -> None:
+    inner = UsageClient([_row(500, 100, 50)])
+    metered = MeteredClient(inner, budget_calls=3)
+    _call(metered)
+    assert metered.priced is False
+    assert metered.usd is None
+    assert metered.usage["prompt_tokens"] == 500
+    assert metered.summary() == {
+        "usd": None,
+        "calls": 1,
+        "usage": {"prompt_tokens": 500, "prompt_cache_hit_tokens": 100, "completion_tokens": 50},
+        "priced": False,
+    }
+
+
+def test_summary_shape_for_a_priced_model() -> None:
+    inner = UsageClient([_row(1_000_000, 0, 0)])
+    metered = MeteredClient(inner, prices=Prices(**FLASH), budget_usd=10.0)
+    _call(metered)
+    summary = metered.summary()
+    assert set(summary) == {"usd", "calls", "usage", "priced"}
+    assert summary["priced"] is True
+    assert summary["calls"] == 1
+    assert summary["usd"] == pytest.approx(0.44)
+    assert summary["usage"] == {"prompt_tokens": 1_000_000, "prompt_cache_hit_tokens": 0, "completion_tokens": 0}
+
+
+def test_prices_from_accepts_manifest_parameters_and_rejects_partial_ones() -> None:
+    assert prices_from(FLASH) == Prices(cache_hit_per_m=0.014, input_per_m=0.44, output_per_m=1.32)
+    assert prices_from({"cache_hit_per_m": 0.014, "input_per_m": 0.44}) is None
+    assert prices_from({"cache_hit_per_m": "0.014", "input_per_m": 0.44, "output_per_m": 1.32}) is None
+    assert prices_from(None) is None
+
+
+def test_client_without_usage_rows_still_counts_calls() -> None:
+    class Bare:
+        def complete(
+            self,
+            *,
+            model: str,
+            messages: list[dict[str, object]],
+            tools: list[dict[str, object]],
+            timeout_seconds: int = 60,
+            json_object: bool = False,
+        ) -> ChatResponse:
+            return ChatResponse(content="ok")
+
+    metered = MeteredClient(Bare(), prices=FLASH, budget_calls=1)
+    _call(metered)
+    assert metered.calls == 1
+    assert metered.usd == 0.0
+    with pytest.raises(BudgetExhausted):
+        _call(metered)