feat: add auto shell detection to atuin init

[vegerot]

Add atuin init (no arguments) and atuin init auto which auto-detect
the current shell using the parent process name, matching the behavior
already available in atuin ai init. Explicit shell names continue to
work as before.

Also update bash and zsh docs to recommend atuin init (auto-detect)
alongside the explicit shell forms.

Closes #3604

[github-actions]

Fossier: Manual Review Requested

@vegerot is a new contributor. A maintainer should review this PR before merging.

Score Breakdown

Total Score: 56.3/100 | Confidence: 100% | Outcome: REVIEW

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bot_signals	False	0.50	0.04
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activity_velocity	2	0.67	0.08
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commit_email	mchcopl@gmail.com	0.80	0.04
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contributor_stars	39	0.78	0.04

[greptile-apps]

Greptile Summary

This PR adds auto shell detection to atuin init. The main changes are:

• atuin init now defaults to an auto shell mode.
• Auto mode maps the detected parent shell to the existing init generators.
• Bash, zsh, integration, and pty-proxy docs now recommend the no-argument form.

Confidence Score: 4/5

The changed CLI path can crash when auto shell detection cannot read the process tree.

• Explicit shell arguments still follow the old init paths.
• The new default path calls a panic-prone detector before returning a recoverable detection error.
• The docs now steer users onto that default path.

crates/atuin/src/command/client/init.rs

Important Files Changed

Filename	Overview
crates/atuin/src/command/client/init.rs	Adds auto shell parsing and routes the resolved shell into static and dotfiles init.
docs/docs/configuration/key-binding.md	Updates key-binding examples to use atuin init without an explicit shell.
docs/docs/faq.md	Updates FAQ examples to use the new auto-detected init form.
docs/docs/guide/installation.md	Adds no-argument init examples for bash and zsh installation.
docs/docs/guide/shell-integration.md	Updates the conditional shell integration example to use auto-detection.
docs/docs/integrations.md	Updates integration guidance to refer to atuin init without shell arguments.
docs/docs/reference/pty-proxy.md	Updates the pty-proxy setup example to use the no-argument init form.

_{Reviews (1): Last reviewed commit: "feat: add auto shell detection to `atuin..." | Re-trigger Greptile}

[greptile-apps]

Auto Detection Can Panic

When atuin init runs without an explicit shell, this line calls the process-tree detector and propagates its expect() panics if the current or parent process is unavailable, such as in a PID namespace or container where Atuin has no visible parent. The new documented default can crash instead of returning the existing shell-detection error.

[Copilot]

Pull request overview

Adds an auto-detection mode to atuin init so users can run atuin init (or atuin init auto) without specifying a shell, aligning the UX with existing auto-detect behavior in atuin ai init. Documentation is updated to recommend the new default invocation in common setup snippets.

Changes:

• Make atuin init default to auto, resolving the shell via parent-process detection.
• Thread the resolved shell through both static and dotfiles-based init paths.
• Update multiple docs pages to use eval "$(atuin init)" (and flag examples like atuin init --disable-ai) instead of explicit atuin init zsh|bash.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
docs/docs/reference/pty-proxy.md	Switches the example to eval "$(atuin init)" for the post-pty-proxy init step.
docs/docs/integrations.md	Updates zsh/bash integration examples to reference atuin init auto-detection.
docs/docs/guide/shell-integration.md	Updates shell-init snippet to use atuin init without an explicit shell.
docs/docs/guide/installation.md	Adds optional auto-detect setup snippets for zsh and bash installation flows.
docs/docs/faq.md	Updates FAQ snippets to use atuin init with flags (no explicit shell arg).
docs/docs/configuration/key-binding.md	Updates key-binding examples to use atuin init with flags (no explicit shell arg).
crates/atuin/src/command/client/init.rs	Implements auto as the default shell argument and resolves it before generating init output.

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