[abhishekgahlot2]

Adds API tool agents: Anthropic and OpenAI agents that act only through HTTP routes an environment declares, run as offline session tool actions.

• Environments declare tools (HttpTool/HttpRoute): a fixed loopback origin, method and path, and JSON shape. Requests are sent by a runner executing as the agent user in the offline namespace, with input supplied from a root-only file. Redirects are not followed. Inline session requests cannot declare tools.
• Every write is held unsettled from dispatch. Grading runs only after the environment's root_tool_settle hook proves the app has finished or dropped every write. Without that proof, the result has no verdict (error_type='unsettled_write'), whatever the score.
• Step verifiers can't be combined with write tools.
• Anthropic tool calls run only after a complete response with stop_reason=tool_use; this check also covers the Anthropic computer-use agent. Cut-off, unfinished or unparsable responses are recorded as incomplete, with what arrived, and never acted on.
• Tool credentials stay root-only and are redacted field by field from every record, including binary bodies. Header credentials and decoded Basic pairs must be ASCII.
• tools, allowed_actions and root_tool_settle load from environment metadata.

Authoring contract (see docs/agents.md):

• An environment with write tools needs a real app-settlement hook, and its correctness is the environment's responsibility.
• Write tools can't use step verifiers.
• Credential values must be ASCII.
• A declared GraphQL or JSON-RPC route allows every body operation the app role permits.

Tests:

• Pre-rebase full suite (-n 4): 2678 passed, 4 failed, 1813 skipped.
• Post-rebase focused run (tests/test_tools.py, tests/agents): 345 passed, 2 baseline CLI-compat failures, 3 skipped.
• Full suite not rerun locally after rebase; CI test jobs (Python 3.10, 3.11, 3.12) passed on this head.

Baseline failures, which also fail on main: 2 test_cli_compat checks against the locally installed CLIs, and 2 computer-use suite counts that read ~/.deepgym/environments.