fix(runtime): sweep node wrapper processes hosting managed agent shims

[wpfleger96]

Problem

codex-acp and claude-agent-acp are npm shims — their OS process name is node, not the binary name. When the Buzz app restarts, buzz-acp dies and the node wrapper is reparented to launchd (PPID=1). The orphan reaper never killed it because process_belongs_to_us() checked the process name against KNOWN_AGENT_BINARIES — "node" was not in the list.

The node wrapper kept the native codex-acp binary alive as its child, and that child had no network_proxy flags (spawned before the update), causing relay network failures for Thufir and any other codex-based agent after an app update.

Fix

Commit 1 — interpreter recognition:
Add KNOWN_SCRIPT_INTERPRETERS = ["node"] and a name_matches_interpreter() helper. Extend both macOS (proc_name()) and Linux (/proc/comm + /proc/exe) variants of process_belongs_to_us() to return true for interpreter names, so the sweep proceeds to process_has_buzz_marker().

Commit 2 — marker check at record-management paths:
Three call sites used process_belongs_to_us() without a subsequent process_has_buzz_marker() check. With node now returning true from process_belongs_to_us(), these sites could falsely act on unrelated node processes (dev servers, build tools) whose PID happened to collide with a stale agent record:

• kill_stale_tracked_processes: would kill the foreign process
• sync_managed_agent_processes: would skip clearing runtime_pid, blocking respawn
• start_managed_agent_process: would skip respawning the agent

Add instance_id: &str to kill_stale_tracked_processes and sync_managed_agent_processes; thread current_instance_id(app) through all 11 call sites. Add process_has_buzz_marker() at all three check sites. The sweep paths already gated on the marker — this brings the record-management paths to the same standard.

Why not add "node" to KNOWN_AGENT_BINARIES? That would sweep all node processes on the machine regardless of ownership — catastrophic false positives.

Future-proofing

KNOWN_SCRIPT_INTERPRETERS is a named constant. Adding python3, deno, or bun support if those become harness runtimes is a one-liner.

Tests

4 new unit tests in runtime/tests.rs:

• name_matches_known_binary_rejects_node — guards against accidentally adding node to KNOWN_AGENT_BINARIES
• name_matches_interpreter_accepts_node — node is recognized as an interpreter
• name_matches_interpreter_rejects_unknown — python3, deno, bun do not match
• name_matches_interpreter_rejects_node_prefix — node_modules, nodejs, node-gyp do not match (exact equality required)

All 40 managed_agents::runtime tests pass.