feat: adapt review budget to diff size

pilot/README-webhook.md

@@ -306,6 +306,11 @@ limit, preserves any output already emitted, and records the cap reason in the
 review body and Langfuse metadata. Environment variables provide deployment-wide
 defaults; repository budget values override them.
 
+Without an explicit repository budget, changed diffs receive adaptive headroom:
+the default 20-step/120K-token budget grows to 40/400K, 60/800K, or 80/1.2M for
+diffs over 200, 800, or 2,000 changed lines. This keeps focused PRs inexpensive
+while allowing broad TypeScript/Go reviews to finish. Hard ceilings still apply.
+
 **Cross-lens dedup:** synthesiser drops duplicates by
 `sha256[:16](path|line|severity|problem[:80])` (matches the feedback DB's
 `posthash`), then promotes multi-lens agreement by one severity step

pilot/review/budget.py

@@ -15,6 +15,13 @@ DEFAULTS = {
     "max_duration_seconds": 480,
 }
 
+PROFILES = (
+    # (changed lines threshold, steps, total tokens, output tokens, seconds)
+    (2_000, 80, 1_200_000, 80_000, 1_800),
+    (800, 60, 800_000, 60_000, 1_200),
+    (200, 40, 400_000, 40_000, 900),
+)
+
 
 @dataclass(frozen=True)
 class Budget:
@@ -63,6 +70,34 @@ class Budget:
             price_target=price_target,
         )
 
+    @classmethod
+    def for_review(cls, config: dict | None, diff: str) -> "Budget":
+        """Choose safe headroom from diff size, unless config is explicit."""
+        if isinstance((config or {}).get("budget"), dict):
+            return cls.from_config(config)
+        changed_lines = _changed_line_count(diff)
+        for threshold, steps, tokens, output, seconds in PROFILES:
+            if changed_lines >= threshold:
+                return cls.from_config({
+                    **(config or {}),
+                    "budget": {
+                        "max_steps": steps,
+                        "max_total_tokens": tokens,
+                        "max_output_tokens": output,
+                        "max_duration_seconds": seconds,
+                    },
+                })
+        return cls.from_config(config)
+
+
+def _changed_line_count(diff: str) -> int:
+    """Count changed lines without treating hunk headers as additions."""
+    return sum(
+        1 for line in diff.splitlines()
+        if (line.startswith("+") and not line.startswith("+++"))
+        or (line.startswith("-") and not line.startswith("---"))
+    )
+
 
 def _env_int(name: str, default: int) -> int:
     try:

pilot/review/opencode.py

@@ -440,7 +440,7 @@ def run_lenses_review(
     always has: prose + a final ```json fence with the legacy schema).
     """
     os.makedirs(WORK_ROOT, exist_ok=True)
-    budget = budget or Budget.from_config(config)
+    budget = budget or Budget.for_review(config, diff)
     budget_state = budget_state or BudgetState(budget)
     workdir = tempfile.mkdtemp(prefix=f"{repo.replace('/', '_')}-{sha[:8]}-", dir=WORK_ROOT)
     keep = bool(os.environ.get("PRAGENT_KEEP_WORK"))
@@ -687,7 +687,7 @@ def run(
             additional_context=additional_context,
         )
 
-    budget = Budget.from_config(config)
+    budget = Budget.for_review(config, diff)
     budget_state = BudgetState(budget)
     os.makedirs(WORK_ROOT, exist_ok=True)
     workdir = tempfile.mkdtemp(prefix=f"{repo.replace('/', '_')}-{sha[:8]}-", dir=WORK_ROOT)