Use global Stack as fallback

[lionello]

Description

Since we removed all occurrences of global.Stack with session.Stack, we ignore the flags (apart from --provider), resulting in accidentally downgrading Portal from HA to affordable.

This PR uses the global.Stack as the fallback stack.

Linked Issues

Checklist

• I have performed a self-review of my code
• I have added appropriate tests
• I have updated the Defang CLI docs and/or README to reflect my changes, if necessary

Summary by CodeRabbit

• Bug Fixes

  • Improved error message for invalid color inputs — shows the invalid value and available options.

• Refactor

  • Consolidated stack and provider configuration into a unified default-based structure to streamline selection.
  • Updated stack resolution and fallback behavior so defaults and interactive selection provide more consistent fallback stacks.

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[coderabbitai]

📝 Walkthrough

Walkthrough

Consolidates stack/provider inputs into a Default stacks.Parameters field on GetStackOpts, updates session loader and stacks.Manager to use that Default, removes a nil-stack-manager fallback, adjusts tests, and tweaks one CLI error message for color parsing. (48 words)

Changes

Cohort / File(s)	Summary
Error messaging src/cmd/cli/command/color.go	Clarified invalid color error text: changed from "color mode not one of %v" to invalid color: %q, not one of %v (quotes the invalid input).
CLI session opts src/cmd/cli/command/session.go	Stop reading separate stack/provider flags into GetStackOpts; now populate GetStackOpts.Default with global.Stack.
Session loader src/pkg/session/session.go	Removed early nil-stack-manager fallback in loadStack; always calls sl.sm.GetStack(ctx, sl.opts.GetStackOpts) and relies on stacks.Manager behavior.
Stacks manager & options src/pkg/stacks/manager.go	GetStackOpts refactor: replaced ProviderID, Stack, AllowStackCreation with Default stacks.Parameters and embedded SelectStackOptions; GetStack now uses Default.Name / Default.Provider and returns Default-based fallbacks.
Tests src/pkg/session/session_test.go, src/pkg/stacks/manager_test.go	Tests updated to use GetStackOpts.Default (Parameters) and new SelectStackOptions paths; removed TestLoadSession_NoStackManager; adjusted expectations for merged stack fields (Region, Variables).

Sequence Diagram(s)

sequenceDiagram
  participant CLI as Client CLI
  participant SL as SessionLoader
  participant SM as StacksManager
  participant DS as DataSource (local/remote)

  CLI->>SL: Build GetStackOpts (Default := global.Stack)
  SL->>SM: GetStack(ctx, GetStackOpts)
  alt Default specified
    SM->>SM: resolve getSpecifiedStack(Default.Name)
    SM->>DS: fetch stack data (local/remote)
    DS-->>SM: stack parameters
    SM-->>SL: Parameters (merged)
  else Interactive
    SM->>SM: getStackInteractively(opts.SelectStackOptions)
    SM-->>SL: Selected Parameters
  end
  SL-->>CLI: return resolved stack Parameters

Loading

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• allow --provider to override default stack #1862: Modifies the same stack-selection surfaces and GetStackOpts/default fallback behavior.
• avoid double stack loading #1800: Alters session.loadStack and stacks.Manager responsibilities for loading stack/environment data.
• Lio/fix default stack #1820: Touches GetStack/GetStackOpts and session loader interactions impacting selection flow.

Suggested reviewers

• jordanstephens

Poem

🐇 I hopped through options, Default in my paw,

Stacks and providers now settled in one law.
No more scattered flags or fallback hazy night—
Sessions call the manager, and everything's airtight.
— a rabbit, nibbling code with delight 🥕

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Use global Stack as fallback' directly and accurately summarizes the main objective of the pull request: restoring global.Stack as the fallback stack when session.Stack is not available.

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✨ Finishing touches

• 📝 Generate docstrings

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.5.0)

level=warning msg="[linters_context] running gomodguard failed: unable to read module file go.mod: current working directory must have a go.mod file: if you are not using go modules it is suggested to disable this linter"
level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@src/pkg/session/session.go`:
- Around line 70-75: When sl.sm is nil in SessionLoader.loadStack, the code
currently unconditionally overwrites sl.opts.Fallback.Name with
stacks.DefaultBeta; change this so you only set fallback.Name =
stacks.DefaultBeta when the existing fallback.Name is empty. Locate
SessionLoader.loadStack and the fallback variable derived from sl.opts.Fallback,
and add a conditional check (e.g., if fallback.Name == "" or equivalent) before
assigning stacks.DefaultBeta, so a user-specified stack name is preserved when
the manager can't be created.

🧹 Nitpick comments (1)

src/pkg/stacks/manager.go (1)

286-291: Track the TODO for selector prefill.

The TODO indicates missing UX behavior (prefill from fallback). Please convert to a tracked issue or implement when feasible.

[edwardrf]

I don't quite like the name fallback, but I don't have a better idea.