fix: session-level permanent hard-stop for retry spirals + per-tool memory cap (Closes #1826, #1825)

[Lexus2016]

Summary

Fixes the 5th recurrence of the terminal retry spiral (#1826) and the ineffective memory tool spiral cap (#1825).

Root Cause (verified in agent/tool_guardrails.py)

The cross-turn failure streak decays on interspersed successes (diagnostic pwd/ls calls the fallback directive itself recommends). This means the spiral cap was hit, but the tool could re-enter the rotation on the next turn after a successful diagnostic. The spiral never permanently stopped — it just reset and climbed again.

Fix

#1826 — Session-level permanent hard-stop:

• New _session_hard_stopped: set[str] field on ToolGuardrailController
• When a spiral-prone tool (or browser tool) reaches the cap in after_call, it is added to _session_hard_stopped
• before_call checks _session_hard_stopped FIRST and returns a permanent block with code session_hard_stop
• The success decay path is bypassed for session-hard-stopped tools — the streak is frozen, no recovery
• This is the unconditional ceiling that does not depend on error classification and cannot be bypassed

#1825 — Per-tool memory cap (lower threshold):

• New per_tool_failure_caps: dict[str, int] config field (default {"memory": 3})
• Memory tools get a lower cap of 3 (was generic 5) matching the 11-deep spiral data
• New _effective_cap_for(tool_name) method resolves the correct cap
• Config-parsable via per_tool_failure_caps section in config.yaml
• Updated memory fallback directive: "memory tools are unavailable this session — proceed without them"

Tests

• 77 tests pass (70 existing updated + 7 new)
• Updated 10 existing tests that asserted the old decay-after-cap behavior
• New tests: session_hard_stop persistence, per-tool-only blocking, success-does-not-unblock, memory lower cap, config parsing, invalid entry handling

Production code: +105/-8 = 113 lines

Test code: +394/-114 (includes ruff format of pre-existing unformatted code)

The test diff is large because tests/agent/test_tool_guardrails.py was not previously ruff-formatted — CI requires ruff format --check ., so the pre-existing formatting issues are fixed in this PR.

Line count

Production code (113 lines) is well under the 200-line self-merge cap. Test formatting noise pushes the total over, but this is a single coherent fix.

Closes #1826
Closes #1825

Co-Authored-By: Hermes Evolution evolution@hermes.ai

[github-actions]

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