Document the SDK-provided tools as stub dirs under strix/tools/

Every agent-facing tool now has a corresponding directory: the
strix-implemented ones already do, and the SDK-provided ones
(exec_command/write_stdin shell, apply_patch, view_image) plus the
sandbox-CLI agent-browser get README-only stubs. Each README names the
implementation source, where the tool is wired up, the strix-specific
config it inherits, and the skill that teaches its usage. Listing
strix/tools/ now gives a new reader the full agent toolset at a glance.

The stub dirs intentionally have no __init__.py — they are not Python
packages, just documentation. Nothing in the codebase auto-discovers
strix.tools.* as packages (all imports are explicit), so the stubs
cannot accidentally affect runtime behavior.

strix/tools/agent_browser/README.md

@@ -0,0 +1,12 @@
+# agent-browser
+
+Browser automation CLI installed in the sandbox image. Driven by the agent
+through `exec_command` (not a function tool).
+
+- **Implementation:** sandbox CLI at
+  `/home/pentester/.npm-global/bin/agent-browser` — npm package
+  `agent-browser@0.26.0` (Vercel), driving Chromium directly.
+- **Strix config:** `containers/Dockerfile` sets `AGENT_BROWSER_*` env
+  (executable path, UA, launch args, screenshot dir).
+- **Skill:** `strix/skills/tooling/agent_browser.md` — **always-loaded**
+  into every agent prompt by `strix/agents/prompt.py:_resolve_skills`.

strix/tools/apply_patch/README.md

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+# apply_patch
+
+SDK-provided file patching tool — the agent's only first-class way to edit
+files in the sandbox. Surfaced to the model as `patch` (renamed via
+`_TOOL_NAME_OVERRIDES` in `strix/agents/factory.py`).
+
+- **Implementation:** `agents.sandbox.capabilities.tools.apply_patch_tool.ApplyPatchTool`
+  (upstream `agents` SDK)
+- **Wired in:** `strix/agents/factory.py` — added per-run via the SDK
+  `Filesystem` capability.

strix/tools/shell/README.md

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+# shell — `exec_command` + `write_stdin`
+
+SDK-provided shell tools wired per-run from the sandbox session. Every CLI
+invocation the agent makes (nmap, ffuf, agent-browser, python3, …) goes
+through `exec_command`. `write_stdin` streams input to a still-running
+process started by an earlier `exec_command` (for interactive prompts).
+
+- **Implementation:** `agents.sandbox.capabilities.tools.shell_tool.ShellTool`
+  (in the upstream `agents` SDK)
+- **Wired in:** `strix/agents/factory.py` — added per-run via the SDK
+  `Shell` capability; `write_stdin` is wrapped to drop the SDK's `pid`
+  arg from the function schema.
+- **Sandbox env:** `http_proxy` / `https_proxy` route every shell child
+  through Caido; `AGENT_BROWSER_*`, `REQUESTS_CA_BUNDLE` etc. come from
+  `containers/Dockerfile`.

strix/tools/view_image/README.md

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+# view_image
+
+SDK-provided tool that loads an image from the sandbox workspace and
+returns it as an image content block for vision-capable models.
+
+- **Implementation:** `agents.sandbox.capabilities.tools.view_image.ViewImageTool`
+  (upstream `agents` SDK)
+- **Wired in:** `strix/agents/factory.py` — added per-run via the SDK
+  `Filesystem` capability.
+- **Strix defaults:** screenshots default to
+  `/workspace/.agent-browser-screenshots/` via `AGENT_BROWSER_SCREENSHOT_DIR`
+  (set in `containers/Dockerfile`; dir is created at container start in
+  `containers/docker-entrypoint.sh`).
+- **Skill:** screenshot workflow lives in `strix/skills/tooling/agent_browser.md`.
+- **Recovery:** vision-not-supported model rejections are auto-recovered
+  via `strix.core.sessions.strip_latest_image_from_session`, invoked from
+  `strix/core/execution.py`.