Release v6.9.0: shell-first exploration, Bash tool, faster agent loop

[code-crusher]

Summary

Ports orbcode's v6.9.0 "faster agent loop" and the shell-first/Bash change (MatterAIOrg/OrbCode#59) to the extension, adapted to this codebase.

• Shell-first exploration: search_files / list_files are no longer offered; the model uses rg/find/ls/git through the shell tool. Prompt sections (tool guide, capabilities, rules, objective, guidelines, env details) updated.
• Read-only commands skip approval in every mode (including "Ask"): src/core/tools/readOnlyCommand.ts, conservative allowlist (no redirects/substitution/-exec/-delete, etc.); isDangerous still wins.
• Bash tool name: model-facing only. Internal name stays execute_command; src/shared/toolAliases.ts translates incoming calls and outgoing history.
• Bash exec shell: the execa path prefers bash (Git Bash on Windows) over the terminal profile; the system prompt states the shell and warns on cmd.exe.
• 6.9.0 pieces that were missing: lean "Working style" prompt block, stale tool-result pruning (40% trigger, last 4 kept, batches of 6, reset on condense), closest-region hint on failed edits.
• Version bumped to 6.9.0 with changelog.

Already present here and so not ported: whitespace/CRLF-tolerant edits, auto-condense, repeat detection, process-tree kill. Not ported: bench/, parallel read-only shell commands (parallel terminals share one interactive ask).

Test plan

• tsc --noEmit (src)
• New specs: readOnlyCommand, staleToolResults; updated tool-contract/prompt specs and 9 prompt snapshots
• Full src vitest: 434 failures both on clean main and on this branch, none new (35 more passing tests)
• Manual: search/list via Bash in all three approval modes, a write command still prompts in "Ask"
• Manual: fish/csh users, Windows with and without Git for Windows
• Manual: resume a task saved before the rename

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