T-1: Docker exec PTY proof-of-concept via bollard

[kirich1409]

Summary

Standalone spike confirming that bollard (Rust Docker client) can reliably manage exec instances with TTY allocation, supporting full cloud-mode terminal sessions.

What Changed

• Added bollard 0.17 dependency to runner/Cargo.toml
• Implemented DockerExecSpike in runner/src/docker_exec_poc.rs (spike code, not production)
• Created docs/docker-exec-spike.md documenting findings and API surface

Acceptance Criteria

• bollard exec attach to running ubuntu container — raw bytes readable
• Resize through resize_exec() works (tput cols reports new value)
• Exit code accessible via inspect_exec() after process termination
• Latency roundtrip < 200ms on localhost (~15–50ms observed)
• PoC documented in docs/docker-exec-spike.md

Findings

✓ Raw byte I/O works reliably via LogOutput stream
✓ Resize applies correctly to container PTY
✓ Exit codes available after process termination
✓ Latency well below 200ms requirement on localhost

All APIs ready for production integration in T-4 (Docker Orchestrator).

Closes #15

[Copilot]

Pull request overview

Standalone spike to validate that the bollard Rust Docker client can create/attach to exec sessions with TTY, resize the PTY, and retrieve exec exit codes—intended to de-risk upcoming “cloud-mode terminal session” work (T-4).

Changes:

• Added bollard as a runner dependency (and updated lockfile).
• Introduced DockerExecSpike PoC module for exec attach/resize/inspect experiments.
• Added a markdown write-up documenting findings and relevant API surface.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
runner/src/main.rs	Declares the new PoC module in the main binary crate.
runner/src/docker_exec_poc.rs	Implements the exec+TTY PoC logic and a basic unit test.
runner/Cargo.toml	Adds bollard = "0.17" dependency.
runner/Cargo.lock	Lockfile updates from introducing bollard and transitive deps.
docs/docker-exec-spike.md	Documents the spike results, APIs used, and next steps.

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