fix(errors): 403 auth rejections no longer read as policy blocks

[saurabhjain1592]

Release-blocking library fix from the getaxonflow/axonflow-enterprise#2861 release-readiness gate. Makes 8.5.2 cut-ready (operator cuts the tag).

Bug

Every agent error envelope carries a literal "blocked" JSON key — a tenant-mismatch rejection is:

{"success":false,"error":"Tenant mismatch","blocked":false}   // HTTP 403

so handleErrorResponse's substring heuristic

case 403:
  if (body.contains("policy") || body.contains("blocked")) {
    throw new PolicyViolationException(errorMessage);
  }

classified every 403 authorization rejection as PolicyViolationException. Callers following the documented pattern (policy block = expected, non-fatal outcome) silently swallowed real auth failures with exit 0 — exactly how examples/basic passed the smoke with a wrong client-id/user-token tenant pairing.

Fix

The 403 branch parses the JSON body (Jackson, already in use) and treats a present blocked boolean as authoritative:

• "blocked":true → PolicyViolationException
• "blocked":false → AuthenticationException (HTTP 403)
• unparseable body, or no blocked boolean → legacy policy-phrase fallback (policy / block_reason; the bare blocked substring no longer counts)

Audited the rest of the method: this was the only substring-classification site — 401 always maps to AuthenticationException; 402/409/429/408/504 key on status code alone.

Tests

• Unit (WireMock): exact live tenant-mismatch envelope → AuthenticationException with message intact; blocked:true envelope → PolicyViolationException; unparseable-body fallback in both directions. Full suite: 1316 tests, 0 failures.
• New live-stack leg runtime-e2e/error_classification_403/ (no skip hatch) asserting both directions through proxyLLMCall.

Live runtime-e2e evidence (enterprise stack, platform v9.6.1, agent :8080)

Against this build (8.5.2 jar):

PASS [tenant-mismatch-403] AuthenticationException: Tenant mismatch
PASS [policy-block-403] PolicyViolationException: Request blocked by policy: Detects stacked DROP TABLE/DATABASE statement
RESULT: PASS (2/2)
EXIT=0

Same leg against the released 8.5.1 jar (proves the bug + the leg's sensitivity):

FAIL: REGRESSION: tenant-mismatch 403 classified as PolicyViolationException (Request blocked by policy: Tenant mismatch) — the "blocked":false envelope must map to AuthenticationException
EXIT=1

Release prep (same PR, per the version-alignment gate)

• pom.xml 8.5.1 → 8.5.2
• CHANGELOG [Unreleased] → [8.5.2] - 2026-07-10 (keeps the fix(examples): basic reads AXONFLOW_USER_TOKEN; async parity e2e #194 example/runtime-e2e content, adds the 403-classification ### Fixed bullet)
• .github/scripts/validate-version-alignment.sh green locally
• Example poms pinned to 8.5.2, mirroring the 8.5.1 release commit's convention (integration CI re-syncs them to the parent version at run time). Note: fix(examples): pin poms to 8.5.1; fail loud on tenant mismatch [skip-runtime-e2e] #196 (open) pins the same lines to 8.5.1 — whichever lands second takes a trivial conflict; if this lands first, fix(examples): pin poms to 8.5.1; fail loud on tenant mismatch [skip-runtime-e2e] #196's pom hunks are superseded.

Refs getaxonflow/axonflow-enterprise#2861.