fix: page keys scroll pane scrollback at zsh and REPL prompts

[HackAttack]

PageUp/PageDown were forwarded to the pane whenever DECCKM (application cursor) was on, assuming only primary-screen pagers enable it, but zsh's line editor also enables DECCKM, as do REPLs such as python3. The result was PageUp scrolling shell history instead of Herdr scrollback.

Bracketed paste discriminates the two: it means the app accepts typed or pasted text at a prompt, so line editors enable it and pagers do not.

Related: #953

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: dc71f042-c209-4de5-8ce0-9bfb4e662355

📥 Commits

Reviewing files that changed from the base of the PR and between 48d8e74 and b13a1a4.

📒 Files selected for processing (1)

• src/pane/terminal.rs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/pane/terminal.rs

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📝 Walkthrough

Walkthrough

The change allows PageUp to scroll host pane history when DECCKM and bracketed paste are active. Regression tests verify local key consumption, scrollback movement, and no shell or PTY input.

Changes

PageUp host scrollback

Layer / File(s)	Summary
Update host scrollback condition src/pane/terminal.rs	plain_page_keys_use_host_scrollback now permits host scrollback with application cursor mode when bracketed paste is enabled. Alternate-screen and mouse-reporting exclusions remain active.
Verify PageUp handling src/pane/terminal.rs, src/app/input/terminal.rs, src/server/headless.rs	Tests verify PageUp host scrolling, local key consumption, and no input forwarding to the shell or PTY.

Estimated code review effort: 2 (Simple) | ~10 minutes

Sequence Diagram(s)

sequenceDiagram
  participant TerminalInput
  participant InputState
  participant HostScrollback
  participant ShellOrPTY
  TerminalInput->>InputState: Process PageUp with DECCKM and bracketed paste enabled
  InputState->>HostScrollback: Consume PageUp and advance pane scrollback
  InputState--xShellOrPTY: Do not forward PageUp bytes

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the fix for PageUp and PageDown behavior in zsh and REPL prompts.
Description check	✅ Passed	The description accurately explains the DECCKM and bracketed-paste behavior that causes the scrollback issue.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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_{Comment @coderabbitai help to get the list of available commands.}

[greptile-apps]

Greptile Summary

This PR refines plain PageUp/PageDown routing so zsh and REPL prompts using both application-cursor and bracketed-paste modes use Herdr scrollback while primary-screen pagers continue receiving page keys.

• Extends the shared terminal input-state predicate with bracketed-paste mode.
• Adds application and headless-server coverage for the shell-like mode combination.
• Preserves forwarding for alternate-screen, mouse-reporting, and pager-like application-cursor states.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/pane/terminal.rs	Refines the shared page-key routing predicate to recognize shell-like DECCKM sessions through bracketed-paste mode and adds direct predicate coverage.
src/app/input/terminal.rs	Adds an application-level test confirming PageUp scrolls the host pane rather than reaching a zsh-like prompt.
src/server/headless.rs	Adds equivalent headless terminal-attach coverage for the revised page-key routing behavior.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    K[Plain PageUp or PageDown] --> A{Alternate screen or mouse reporting?}
    A -- Yes --> P[Forward key to pane]
    A -- No --> C{Application cursor enabled?}
    C -- No --> H[Use Herdr scrollback]
    C -- Yes --> B{Bracketed paste enabled?}
    B -- Yes --> H
    B -- No --> P

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_{Reviews (3): Last reviewed commit: "test: update page key state fixture" | Re-trigger Greptile}

[ogulcancelik]

ty!