[kaluli123123]

Summary

• Keep every reported display slice on a UTF-8 boundary and calculate remote label offsets in character units.

Closes #118.

Root cause

Arbitrary byte slices in the session picker and terminal short IDs could split UTF-8; remote label offsets mixed bytes and characters.

Test plan and evidence

• RED before repair: Picker panicked at byte 7 inside é; two terminal flows panicked at byte 8 inside é.
• Focused: CLI library 17 passed; tui_flow_snapshots 15 passed, including 3 new regression tests (the picker test covers 3 cases).
• Runtime: cargo-run temporary example invoked the public terminal loop against a virtual terminal: status 1234567 | /help, child subscription [1234567] ⚡watch: changed, picker 123456….
• Rust formatting, workspace Clippy with warnings denied, and all-target compilation passed through ./check.bash.
• cargo test --locked --all-targets --no-fail-fast: 358 passed, 7 failed, 0 ignored. The exact same seven failures independently reproduced on clean base 1abc6fcff1f186124f924b56aa92c3a3684c90c5 (355 passed, 7 failed, 0 ignored), across tui_reflow_snapshots (6) and tui_submit_wrap_snapshots (1). No snapshots or thresholds were changed.
• cargo test --locked --doc: 45 passed, 1 ignored.
• Independent read-only review: no blocking findings.

Changed files

• crates/infinity-agent-cli/src/session_picker.rs
• crates/infinity-agent-cli/src/terminal.rs
• crates/infinity-agent-cli/tests/tui_flow_snapshots.rs
• docs/docs/infinity-code/overview.md

Remaining gates

Draft: required full checks are not green. Remote CI and maintainer review remain outstanding. Docs/UI Prettier were skipped by the repository script because node_modules are absent; optional browser e2e and THIRD-PARTY verification were not reached after the test gate failed. No live model account was used.

One independent commit from base 1abc6fcff1f186124f924b56aa92c3a3684c90c5. No dependency or wire-protocol changes. No merge, deployment, or Issue closure performed.