fix(auth): preserve isolated credentials on decryption failure

[mandalorianuy]

Description

Preserve isolated encrypted credentials and token caches when decryption fails, fail closed instead of silently authenticating with another credential source, and default custom config directories to profile-local file key storage unless the backend is explicitly overridden.

Source implementation commit: d594aec746955373976619876e95f237872ab0db.
Delivery commit: 27619dc7ccbf46f7cdf85d6c54c5bcc3a1ad42f2 (cherry-picked with traceability).

Dry Run Output:
Not applicable; this is an authentication and credential-storage fix with no API request or helper command change.

Validation

• cargo fmt --all -- --check
• cargo test -p google-workspace-cli --bin gws auth::tests — 23 passed
• cargo test -p google-workspace-cli --bin gws credential_store::tests — 28 passed
• cargo test -p google-workspace-cli — 703 passed
• cargo clippy -p google-workspace-cli --bin gws -- -D warnings
• cargo build -p google-workspace-cli
• git diff --check
• pre-push hook — cargo check, google-workspace 82 tests, CLI 703 tests
• Changeset added: .changeset/preserve-undecryptable-credentials.md

The final branch is based on origin/main a3768d0e82ad83cca2da97724e46bea4ff0e6dbd and changes only the changeset, auth.rs, and credential_store.rs. No Google Workspace APIs, credentials, scopes, users, Sheet, or email were touched; human review and merge remain pending.

[changeset-bot]

🦋 Changeset detected

Latest commit: 27619dc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@googleworkspace/cli	Patch

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request improves the robustness and security of the credential management system. By changing the behavior to fail closed on decryption errors, it prevents potential silent authentication issues. Additionally, it introduces smarter defaults for key storage backends when using isolated configuration directories, enhancing support for multi-profile environments.

Highlights

• Credential Decryption Failure Handling: Modified the authentication flow to preserve encrypted credentials and token caches upon decryption failure, ensuring the system fails closed rather than silently falling back to other identity sources.
• Default Key Storage Backend: Updated the keyring backend logic to default to profile-local file storage when a custom configuration directory is used, preventing unintended sharing of OS-keyring entries across profiles.

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[gemini-code-assist]

Code Review

This pull request updates the CLI's credential handling to fail closed upon decryption failure, preserving the encrypted credentials and token caches instead of deleting them and falling through to other sources. It also updates the keyring backend selection to default to file-based storage when a custom configuration directory is specified, preventing profile conflicts. As there are no review comments, I have no feedback to provide.