fix: require --stdin to read instance types from stdin

[riac03]

Root Cause

brev create was automatically trying to read stdin in non-interactive environments. When stdin was an open pipe that never closed, the CLI kept waiting indefinitely, resulting in no output, no error, and no instance being created. This could happen even when --type was already provided.

Solution

Updated the stdin handling so that --type takes priority and does not read stdin. Reading piped input is now explicit through the --stdin flag. If stdin is requested but no input is received, the CLI returns a clear error instead of hanging silently.
This ensures brev create either proceeds normally or exits with a clear error, rather than getting stuck indefinitely.

Summary by CodeRabbit

• New Features

  • Added explicit --stdin support for creating GPU instances from piped JSON or table data.
  • Added validation for empty piped input and clean handling of interrupted input.
  • Explicit instance types take precedence over piped data.

• Documentation

  • Updated CLI examples and workflows to include --stdin when passing piped search results to instance creation and opening commands.

• Bug Fixes

  • Improved handling when stdin status cannot be determined.

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Walkthrough

The GPU create command now reads piped instance data only when --stdin is specified. It supports JSON and table input, handles empty or interrupted input, and updates related command examples.

Changes

GPU create stdin flow

Layer / File(s)	Summary
Opt-in stdin parsing and validation pkg/cmd/gpucreate/gpucreate.go, pkg/cmd/gpucreate/gpucreate_test.go, pkg/cmd/util/piping.go	The create command registers --stdin, parses JSON or table input, gives --type precedence, handles empty or interrupted input, and adds test coverage. Stdin status errors now return false.
Updated piped workflow examples docs/PRD-composable-cli.md, pkg/cmd/gpusearch/gpusearch.go, pkg/cmd/open/open.go, pkg/cmd/shell/shell.go	Piped create examples now include --stdin.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant User
  participant gpucreate
  participant parseInstanceTypes
  participant Stdin
  User->>gpucreate: invoke create --stdin
  gpucreate->>parseInstanceTypes: parse with stdin enabled
  parseInstanceTypes->>Stdin: read piped instance data
  Stdin-->>parseInstanceTypes: JSON or table input
  parseInstanceTypes-->>gpucreate: parsed instance specifications

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Suggested reviewers: thefong

Merge Risk: 🟡 Moderate · up to ee71d

Some stdin inputs can unexpectedly select a default GPU, while one documented pipeline fails validation. The fallback should be blocked before merge.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 6 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: stdin is read only when the --stdin flag is provided.
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.

Full details: Docstring Coverage

Explanation

Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 6 files. (1 skipped: 1 unsupported.)

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---

_{A rabbit pipes data through the CLI bright
--stdin tells create to read it right
JSON and tables hop into view
Empty input gets an error too
The GPU path now knows what to do}

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

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Actionable comments posted: 2

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Inline comments:
In `@pkg/cmd/gpucreate/gpucreate.go`:
- Line 803: Update resolveInstanceTypes to return a validation error when
readStdin is enabled and the parsed specs slice is empty, before falling back to
the default GPU search; preserve the existing return path for non-empty input
and non-stdin resolution.

In `@pkg/cmd/gpusearch/gpusearch.go`:
- Line 1149: Update the gpusearch usage example to provide an explicit create
name before the --stdin flag, changing the brev create invocation from an
unnamed form to the named form while preserving the rest of the pipeline.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Enterprise

Run ID: 741d53a3-e8c7-44bd-8697-a2296dc32a75

📥 Commits

Reviewing files that changed from the base of the PR and between 524220a and ee71d33.

📒 Files selected for processing (7)

• docs/PRD-composable-cli.md
• pkg/cmd/gpucreate/gpucreate.go
• pkg/cmd/gpucreate/gpucreate_test.go
• pkg/cmd/gpusearch/gpusearch.go
• pkg/cmd/open/open.go
• pkg/cmd/shell/shell.go
• pkg/cmd/util/piping.go

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