fix(resource): expose standard budget error contract

CHANGELOG.md

@@ -23,7 +23,7 @@ All notable changes to OriginWeave are documented in this file. The format follo
 - Credential-free TLS evidence containing canonical origin, TCP peers, reference identity, TLS version, cipher-suite identifier, selected ALPN or explicit absence, leaf certificate and SPKI hashes, server-presented certificate hashes and bounds, trust-bundle identity and hash, validity interval, fixed verification time, revocation configuration, and measured handshake duration.
 - Credential-free connection and redirect evidence containing canonical addresses, destination classes, target digests, hop numbers, and approved-address counts.
 - Credential-free verified TCP evidence containing the logical origin, requested socket, observed peer, destination class, successful attempt number, and per-attempt timeout.
-- Standard `Display` and `std::error::Error` contracts for destination, redirect, digest, direct-network, and TLS failures, including preserved destination-policy, rustls, and operating-system sources where applicable.
+- Standard `Display` and `std::error::Error` contracts for destination, redirect, digest, direct-network, TLS, and resource-budget failures, including preserved destination-policy, rustls, and operating-system sources where applicable.
 - Real loopback TCP integration proof plus deterministic timeout, refusal, retry, peer-inspection, peer-mismatch, canonicalization, IPv6 metadata, and single-use replay tests.
 - Real loopback rustls integration covering trusted DNS SAN, Common-Name fallback rejection, wrong-name and untrusted-root rejection, fixed-time expiry and not-yet-valid failures, exact IPv4 and IPv6 SANs, TLS 1.2/TLS 1.3, required and optional ALPN, and transport-origin binding.
 - Cumulative interactive-first RAM, VRAM, batch, local-model, admission, pause, and compositor-pressure mitigation plans, including active-consumer reduction at exact hard limits.

crates/originweave-resource/src/lib.rs

@@ -9,6 +9,8 @@
 #![forbid(unsafe_code)]
 #![deny(missing_docs)]
 
+use std::fmt;
+
 /// A validation error in a resource budget.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum BudgetError {
@@ -18,6 +20,19 @@ pub enum BudgetError {
     SoftExceedsHard,
 }
 
+impl fmt::Display for BudgetError {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::ZeroLimit => formatter.write_str("resource budget limits must be nonzero"),
+            Self::SoftExceedsHard => {
+                formatter.write_str("resource budget soft limits must not exceed hard limits")
+            }
+        }
+    }
+}
+
+impl std::error::Error for BudgetError {}
+
 /// Validated resource limits for one agent task.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub struct ResourceBudget {

crates/originweave-resource/tests/error_contract.rs

@@ -0,0 +1,21 @@
+use originweave_resource::BudgetError;
+use std::error::Error as _;
+
+#[test]
+fn budget_errors_expose_stable_standard_error_contract() {
+    let cases = [
+        (
+            BudgetError::ZeroLimit,
+            "resource budget limits must be nonzero",
+        ),
+        (
+            BudgetError::SoftExceedsHard,
+            "resource budget soft limits must not exceed hard limits",
+        ),
+    ];
+
+    for (error, expected_message) in cases {
+        assert_eq!(error.to_string(), expected_message);
+        assert!(error.source().is_none());
+    }
+}