fix(runtime): update shell session wire protocol

[priyasingh2111]

Description

Remove the 0x03 metadata frame dependency and 0xFF close frame send from the shell connection flow to align with the K8s wire protocol.

Changes:

1. Removed encodeClose() method from ShellFramer — CLI already uses ws.close() for detach, this was dead code
2. Removed confirmation frame blocking wait — connection is now ready immediately after WebSocket opens + shellId read from the 101 upgrade
   header (eliminates up to 10s wait)
3. Removed reconnected / bytesDropped from ShellConnection — these were populated by the confirmation frame we no longer wait for
4. Confirmation frames silently swallowed during iteration — forward-compatible if server still sends them

Exit codes, keepalive/reconnect, and Ctrl+] detach all continue to work unchanged.

Related Issue

Closes #

Documentation PR

N/A — no user-facing documentation changes needed.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Results:

• 6,068 unit tests pass (422 test files)
• 0 lint errors (33 pre-existing warnings unchanged)
• Format check clean
• Live integration tests: 10/10 against prod (connection in ~3s, no 10s wait)

Breaking changes:

• ShellConnection.reconnected and ShellConnection.bytesDropped no longer exist
• ShellReconnectOptions.onBytesDropped and onNewSession callbacks removed
• ShellFramer.encodeClose() method removed
• Old clients will hard-fail (10s timeout then error) when the server stops sending the 0x03 confirmation frame — this is an accepted breaking change
  per team decision (no protocol negotiation)

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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terms of your choice.

[agentcore-devx-automation]

Claude Security Review: no high-confidence findings. (run)