fix(runtime): polish invoke TUI errors and sessions

[aidandaly24]

Summary

• surface available error names and messages for every non-abort Runtime lookup, invocation, and response-stream failure
• render modeled AWS service failures as a structured type, HTTP status, message, and request ID while preserving redaction for arbitrary transport causes
• generate and display a Runtime session ID before the first TUI send, while honoring --session-id
• remove the redundant JSON payload heading and trailing response whitespace before settled metadata

Testing

• bun test src/core/core.test.ts src/handlers/runtime/invoke/invoke.screen.test.tsx (60 pass)
• bun run typecheck
• bun run lint:check
• bun run format:check
• TUI Harness: successful live invocation without --session-id; generated ID persisted in request and response
• TUI Harness: intentionally short session ID rendered the AWS ValidationException type, HTTP status, complete message, and request ID on separate lines
• TUI Harness: final SSE event now renders directly above session metadata while preserving spacing between events
• bun test src: the only failures were two unchanged src/io/exec.test.ts subprocess-output assertions that reproduce when run alone in this environment

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.29%. Comparing base (ae6e810) to head (32b42f6).
⚠️ Report is 1 commits behind head on refactor.

Additional details and impacted files

@@            Coverage Diff            @@
##           refactor    #1930   +/-   ##
=========================================
  Coverage     96.28%   96.29%           
=========================================
  Files           245      245           
  Lines         12105    12130   +25     
=========================================
+ Hits          11655    11680   +25     
  Misses          450      450           

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[AlexanderRichey]

Approved with a couple comments we might want to address in a follow up.

[AlexanderRichey]

Should this be an AgentCoreError?

[AlexanderRichey]

Is all of this complexity necessary? Why not simply throw the error? All of these details should already be handled in the error message, no? If they're not handled, then extracting this complexity into a reusable helper would help to simplify the main flow at this level.