Fix DinD compose ACP: use Daytona PTY WebSocket for live agent pipes

[xdotli]

Summary

• New DaytonaPtyProcess class that uses Daytona SDK's WebSocket PTY API instead of SSH for DinD compose tasks
• SSH pipes break through the DinD→compose exec chain (Process closed stdout rc=None). WebSocket PTY maintains the connection.
• Echo-resistant ACP response matching in client.py (filter echoed requests by checking for method field absence)
• skills_dir: "auto" support in Job for per-task skill resolution (needed after skillsbench PR #720 removed COPY skills from Dockerfiles)

How it works

Old (SSH, breaks):
local → SSH → DinD VM → docker compose exec -T → container → agent
                         ↑ stdout pipe dies here

New (PTY WebSocket):
local → WebSocket → DinD VM PTY → docker compose exec -i -T → container → agent
                    ↑ persistent interactive session

1. Outer PTY (Daytona WebSocket): keeps connection alive through DinD
2. Inner -T (compose exec): disables TTY inside container so agent gets clean stdio
3. Marker-based startup: drains shell output before ACP handshake
4. Auto-detection: _acp_run.py detects DinD → uses PTY transport automatically

Test results

Task	Before	After
pedestrian-traffic-counting	rc=None, 0 tools	reward=0.014, 7 tools
gh-repo-analytics	rc=None, 0 tools	reward=0.0, 11 tools
pg-essay-to-audiobook	rc=None, 0 tools	34 tools (PTY timeout — needs longer readline)

Test plan

• pedestrian-traffic-counting: agent runs, produces reward
• gh-repo-analytics: agent runs, 11 tool calls
• pg-essay-to-audiobook: agent runs 34 tool calls (readline timeout needs increase)
• Non-compose tasks unaffected (PTY only used for DinD)

Ref: #192

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