fix(#1188): browser_navigate spiral cap regression — 15-deep spirals

[Lexus2016]

Summary

Fixes #1188 — browser_navigate failures regress with 15-deep consecutive spirals across 30 sessions, despite the existing cap=3.

Root Cause

Two independent root causes prevented the cap from enforcing:

1. bot_detection_warning misclassified as success (agent/display.py)

browser_navigate returns {"success": true, "bot_detection_warning": "..."} when it successfully navigates to a bot-detection/Cloudflare/captcha page (the browser-level navigation succeeded, but the page is a blocked page). The failure classifier _detect_tool_failure saw success: true and returned failed=False — so the guardrail counter never incremented. The model retried 15× against a blocked page that will never load properly.

Fix: Added a bot_detection_warning check to both _detect_tool_failure (production path) and classify_tool_failure (fallback classifier) — when success=true AND bot_detection_warning is present, classify as [bot detection] failure.

2. Intermittent success resets cross-turn streak (agent/tool_guardrails.py)

A single successful navigation (e.g., to a different, fast-loading page between failing attempts) fully cleared _cross_turn_tool_failure_counts via pop(), resetting the streak to 0. The cap never accumulated because the pattern fail, succeed, fail, succeed, fail... kept the counter below the threshold.

Fix: Decay the cross-turn streak by 1 on success instead of clearing it. Multiple consecutive successes still drain to 0 (a genuinely recovered backend is not penalized), but a fail/succeed/fail pattern now accumulates toward the cap and eventually halts.

Verification

• E2E reproduction confirmed both root causes (standalone scripts, not committed)
• scripts/run_tests.sh tests/agent/test_tool_guardrails.py — 65/65 tests pass
• scripts/run_tests.sh tests/agent/test_display.py tests/tools/test_browser_navigate_fallback.py tests/agent/test_tool_result_classification.py — 75/75 pass
• 4 new tests + 2 updated tests covering both fixes

Files Changed

• agent/display.py — _detect_tool_failure: classify bot_detection_warning as failure
• agent/tool_guardrails.py — classify_tool_failure: mirror the bot_detection check; after_call: decay cross-turn streak by 1 on success instead of clearing
• tests/agent/test_tool_guardrails.py — 4 new + 2 updated tests