feat(dev): supervise every runtime in project dev

[tejaskash]

Review after #1980

What this does

agentcore project dev without --agent runs all of the project's runtimes at once. Each agent's output is attributed ([orders] ... in the terminal, an agent field in NDJSON); one agent crashing reports its failure and leaves the others running; Ctrl-C tears the whole set down. Selecting one runtime (--agent, or a single-runtime project) keeps the direct path where a crash fails the command — scripts and CI rely on that exit code.

How

DevSupervisor (core/dev/supervisor.ts) owns per-agent lifecycle: an abort scope per agent chained to the command signal, a per-agent state machine (idle/starting/running/failed) with start dedup, TCP readiness probing, and one merged attributed event stream. It's also what the Inspector UI slice (next PR) drives via its start-on-demand API. Ports resolve sequentially — concurrent resolution raced two HTTP agents onto the same port.

Verification

• Supervisor: state machine, dedup, retry-after-failure, merge, crash isolation, abort chaining.
• Handler with fake runners + fake collector, including runners that bind real TCP listeners so the readiness probe runs for real.
• End to end: built the bundle, scaffolded a project, added a second runtime to agentcore.json, ran project dev — both agents started on distinct ports with attributed logs, both answered real Bedrock invocations, and the trace directory holds spans for both service names (per-runtime OTEL_SERVICE_NAME verified end to end). SIGTERM exits 130.

tsc/lint/format clean.

[tejaskash]

Both addressed:

• Unbounded poll — waitForPort has a 120s deadline now; a never-binding child fails with a clear message instead of blocking. Tested dead + live ports.
• Leaked abort listeners — early setup failures unchain the parent-abort listener like every other exit path. Tested across three failed retries.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.24%. Comparing base (f38b18d) to head (7b4b60b).

Additional details and impacted files

@@             Coverage Diff              @@
##           refactor    #2041      +/-   ##
============================================
+ Coverage     97.22%   97.24%   +0.02%     
============================================
  Files           391      392       +1     
  Lines         23677    23894     +217     
============================================
+ Hits          23019    23236     +217     
  Misses          658      658              

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