feat: make headless terminal size configurable

[ogulcancelik]

Summary

• use a 120×40 virtual terminal when no client is attached
• add reloadable server.headless_cols and server.headless_rows settings
• preserve attached-client sizing and existing detached PTY sizes
• document the headless fallback and cover configured headless pane creation

Refs #2828.

Validation

• just check
• just bench-render-scale
  • 15 background workspaces: 1.07× one-pane median
  • 15 active panes: 1.16× one-pane median

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

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Run ID: 66b1c6fd-bd58-4210-93d5-4abb470237c9

📥 Commits

Reviewing files that changed from the base of the PR and between f8125c4 and b4fa665.

📒 Files selected for processing (1)

• docs/next/CHANGELOG.md

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

• docs/next/CHANGELOG.md

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📝 Walkthrough

Walkthrough

The server now supports configurable headless terminal dimensions. Defaults are 120 columns by 40 rows. Configuration validation, live reloads, runtime sizing, documentation, and integration tests cover the behavior.

Changes

Headless terminal sizing

Layer / File(s)	Summary
Configuration contract and validation src/config.rs, src/config/model.rs, src/config/io.rs, src/main.rs, docs/next/website/src/..., docs/next/CHANGELOG.md	Adds [server] settings for headless_cols and headless_rows, defaults of 120×40, validation for zero values, live loading, configuration templates, and documentation.
Application configuration state src/app/mod.rs, src/app/state.rs	Initializes AppState.headless_size from configuration and updates it during live reloads. Invalid dimensions produce diagnostics and preserve the current size. Pane size estimation uses the configured dimensions when no pane geometry exists.
Headless server sizing and integration coverage src/server/headless.rs, tests/detach_reattach.rs, tests/api_ping.rs	Uses the configured size when no client is attached, refreshes it after reloads, and verifies default, attached, detached, and custom pane dimensions. The API ping test requests 50 recent lines.

Estimated code review effort: 3 (Moderate) | ~25 minutes

Merge Risk: ⚪ Minimal · up to b4fa6

The PR adds configurable sizing for headless terminals while preserving attached-client and detached PTY behavior; no actionable merge-blocking risk remains after normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant Config
  participant AppState
  participant HeadlessServer
  participant PanePTY
  Config->>AppState: Load headless_cols and headless_rows
  AppState->>HeadlessServer: Provide headless_size
  HeadlessServer->>PanePTY: Apply effective_size without a client
  Config->>AppState: Reload server dimensions
  AppState->>HeadlessServer: Refresh headless_size

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: configurable headless terminal sizing.
Description check	✅ Passed	The description accurately summarizes the configurable headless sizing, reload behavior, preservation rules, documentation, and validation.
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
• Commit unit tests in branch issue/2828-headless-size

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[ogulcancelik]

@greptileai

[greptile-apps]

Greptile Summary

The PR adds reloadable headless terminal dimensions while retaining attached-client authority and preserving existing PTY sizes after detach.

• Adds validated server.headless_cols and server.headless_rows configuration with 120×40 defaults.
• Uses the configured fallback for initial pane creation and recomputes virtual layout when the final client detaches.
• Documents the settings and adds unit and real-PTY regression coverage.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/server/headless.rs	Propagates configured fallback dimensions into the headless server and safely recomputes detached view geometry without resizing existing PTYs.
src/app/state.rs	Stores the configured headless size and uses it when no computed pane geometry exists.
src/app/mod.rs	Initializes and reloads headless dimensions while retaining current values when the server section is invalid.
src/config.rs	Adds defaults and nonzero validation for headless terminal dimensions.
src/config/io.rs	Registers and live-loads the new top-level server configuration section.
src/config/model.rs	Defines the server configuration model, defaults, parsing coverage, and validation tests.
tests/detach_reattach.rs	Adds real-PTY coverage for initial headless creation and creation after detaching a differently sized client.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  Config[server.headless_cols / headless_rows] --> State[AppState headless_size]
  State --> Server[HeadlessServer headless_size]
  Client{Client attached?}
  Client -->|Yes| Attached[Use attached-client geometry]
  Client -->|No| Headless[Recompute virtual headless layout]
  Headless --> NewPane[Seed newly created pane PTY]
  Attached --> ExistingPTY[Resize shared attached runtime]
  Headless -. no resize .-> ExistingPTY

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[coderabbitai]

Actionable comments posted: 1

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: fc41ed59-d8ab-484e-b5ff-148adb7bb8a5

📥 Commits

Reviewing files that changed from the base of the PR and between 20cf796 and f533492.

📒 Files selected for processing (2)

• src/server/headless.rs
• tests/detach_reattach.rs

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

• src/server/headless.rs