feat(terminal): collapse subagent task_ids to shared container (#16177)

Before: delegate_task children each allocated their own terminal
sandbox keyed by child task_id. Starting extra containers (or Modal
sandboxes / Daytona workspaces) is expensive, and the subagent's work
is invisible to the parent — files written by the child in its
container don't exist in the parent's when the subagent returns.

After: a single `_resolve_container_task_id` helper maps any
tool-call task_id to "default" UNLESS an env override is registered
for it. The parent agent and all delegate_task children therefore
share one long-lived sandbox — installed packages, cwd, /workspace
files, and /tmp scratch carry over freely between them.

RL and benchmark environments (TerminalBench2, HermesSweEnv, ...)
opt in to isolation via `register_task_env_overrides(task_id, {...})`;
those task_ids survive the collapse and get their own sandbox,
preserving the per-task Docker image behavior these benchmarks rely on.

file_state / active-subagents registry / TUI events still key off the
original child task_id, so the 'subagent wrote a file the parent read'
warning and UI per-subagent panels keep working.

Tradeoff: parallel delegate_task children (tasks=[...]) now share one
bash/container. Concurrent cd, env-var mutations, and writes to the
same path will collide. If that bites a specific workflow, the
subagent can opt back into isolation via register_task_env_overrides.

Applied at four lookup sites:
- tools/terminal_tool.py terminal_tool() and get_active_env()
- tools/file_tools.py _get_file_ops() and _get_live_tracking_cwd()
- tools/code_execution_tool.py _get_or_create_environment()

Docs: website/docs/user-guide/configuration.md updated to reflect the
shared-container reality and document the RL/benchmark carve-out.
Tests: tests/tools/test_shared_container_task_id.py (9 cases).

website/docs/user-guide/configuration.md

@@ -146,9 +146,9 @@ terminal:
 
 **Requirements:** Docker Desktop or Docker Engine installed and running. Hermes probes `$PATH` plus common macOS install locations (`/usr/local/bin/docker`, `/opt/homebrew/bin/docker`, Docker Desktop app bundle).
 
-**Container lifecycle:** Hermes reuses a single long-lived container (`docker run -d ... sleep 2h`) for every terminal and file-tool call made by the top-level agent, across sessions, `/new`, and `/reset`, for the lifetime of the Hermes process. Commands run via `docker exec` with a login shell, so working-directory changes, installed packages, and files in `/workspace` all persist from one tool call to the next. The container is stopped and removed on Hermes shutdown (or when the idle-sweep reclaims it).
+**Container lifecycle:** Hermes reuses a single long-lived container (`docker run -d ... sleep 2h`) for every terminal and file-tool call, across sessions, `/new`, `/reset`, and `delegate_task` subagents, for the lifetime of the Hermes process. Commands run via `docker exec` with a login shell, so working-directory changes, installed packages, and files in `/workspace` all persist from one tool call to the next. The container is stopped and removed on Hermes shutdown (or when the idle-sweep reclaims it).
 
-Subagents (`delegate_task`) and RL rollouts get their own isolated containers keyed by `task_id` — only the top-level agent shares the `default` container.
+Parallel subagents spawned via `delegate_task(tasks=[...])` share this one container — concurrent `cd`, env mutations, and writes to the same path will collide. If a subagent needs an isolated sandbox, it must register a per-task image override via `register_task_env_overrides()`, which RL and benchmark environments (TerminalBench2, HermesSweEnv, etc.) do automatically for their per-task Docker images.
 
 **Security hardening:**
 - `--cap-drop ALL` with only `DAC_OVERRIDE`, `CHOWN`, `FOWNER` added back