feat: Keying stack output addresses by iteration key

[yhakbar]

Description

Adds support for addressing components by address despite being expanded.

e.g.

# One element of a unit expanded over for_each
terragrunt stack output 'aurora["web"].role' --experiment block-iteration

# One element of a unit expanded over count, narrowed to the bare value
terragrunt stack output 'shard[0].role' --format raw --experiment block-iteration

TODOs

Read the Gruntwork contribution guidelines.

• I authored this code entirely myself
• I am submitting code based on open source software (e.g. MIT, MPL-2.0, Apache)
• I am adding or upgrading a dependency or adapted code and confirm it has a compatible open source license
• Update the docs.
• Update the changelog in the docs.
• Run the relevant tests successfully, including pre-commit checks.
• This change is backwards compatible.
• If this change is not forwards compatible (e.g. a new feature), it is gated behind a feature flag.

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Project	Deployment	Actions	Updated (UTC)
terragrunt-docs	Ready	Preview	Aug 21, 2026 7:22pm

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📥 Commits

Reviewing files that changed from the base of the PR and between 286a33c and d0a941d.

📒 Files selected for processing (9)

• internal/cli/commands/stack/filter_outputs_test.go
• internal/cli/commands/stack/stack.go
• internal/stacks/output/nest_outputs_test.go
• internal/stacks/output/output.go
• pkg/config/stack.go
• test/fixtures/stacks/expansion-outputs/live/terragrunt.stack.hcl
• test/fixtures/stacks/expansion-outputs/units/app/main.tf
• test/fixtures/stacks/expansion-outputs/units/app/terragrunt.hcl
• test/integration_stack_expansion_output_tf_test.go

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