fix: resolve safe issues from open-issue triage

[1jehuang]

Summary

• fix nine clear, reproducible issues found during open-issue triage
• add focused regression coverage for each changed behavior
• keep platform-sensitive and design-heavy reports out of this PR

Issues

Fixes #1073, #1072, #1071, #1068, #1060, #1053, #1052, #1051, and #1050.

Validation

• cargo fmt --all -- --check
• focused jcode-base Grok auth tests
• full jcode-provider-openrouter-runtime tests
• full jcode-provider-copilot-runtime tests
• full jcode-tui-mermaid library tests
• cargo check -p jcode-tui

--- — Jcode agent (automated triage), on behalf of @1jehuang

[greptile-apps]

Greptile Summary

This change updates Copilot GPT-5.6 streaming, authentication refresh behavior, named-provider image capability defaults, remote session-state preservation, and Mermaid rendering in tmux.

The Copilot GPT-5.6 failure hypothesis was disproved with a loopback execution of the real completion path: it sent a Responses API request with the expected input, instructions, tools, output-token limit, and streaming fields, then translated representative text, tool, usage, and completion events into the shared stream contract.

The native tmux Sixel rendering failure hypothesis was also disproved. Focused rendering checks confirmed that the native-capability path produces direct Sixel output without tmux passthrough wrapping, and that the path requires both server and client Sixel support.

No actionable defects were found.

Confidence Score: 5/5

The reviewed provider-streaming and terminal-image paths behaved correctly in focused executable checks.

The highest-impact changed behaviors were exercised directly: a loopback Copilot Responses request with representative streamed events, and construction and rendering of the native tmux Sixel protocol path. Neither check produced a defect.

Files Needing Attention: No files require follow-up from this review. Native tmux behavior was validated at the protocol-output level because tmux itself is not installed in the environment.

T-Rex Logs

What T-Rex did

• Ran a loopback regression test for the complete_gpt_5_6_uses_responses_route_and_translates_sse_contract against a local HTTP server, exercising the real complete() path with POST /responses (input, instructions, tools, max_output_tokens, stream) and validating the SSE translation.
• Ran and observed native tmux Sixel tests; one test passed with no failures, and the capability predicate test passed, confirming that the native-capability branch emits direct Sixel sequences and does not use a tmux passthrough wrapper.
• Adjusted the exact-filter invocation after an initial misstep, and ran the after-run and final-trace tests; both executed one loopback test and passed, with synthetic bearer auth isolating credentials.
• Validated the direct-path Sixel tests for native tmux validation; the direct-output test passed (1 passed, 0 failed) and the server-capacity test passed; tmux was not installed, so tests ran without a tmux session.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "fix: preserve Mermaid diagrams in native..." | Re-trigger Greptile}

[manoj402kumar]

@1jehuang can you plese check #1029 and make the isse resloved