feat: add previous account switch

[Loongphy]

Summary

• Add cd - style previous-account switching via codex-auth - and codex-auth switch -.
• Persist previous_active_account_key in registry schema 4 and normalize schema 4 files missing it.
• Preserve previous-account state during same-account switches and active-account removal replacement; clear it only when the recorded previous account is removed.

Validation

• HOME=/tmp/previous-account-switch zig build run -- list
• HOME=/tmp/previous-account-switch zig build test
• git diff --check

Risks

• Registry persistence now writes previous_active_account_key while staying on schema_version = 4 because this schema has not shipped yet.
• Previous switch depends on recorded account keys; it fails without mutation when the recorded previous account is missing.

PR Loop Status

• Latest push creates the feature branch and initial PR.
• CI status pending.
• No review comments have been addressed yet.
• No comments intentionally left unresolved.

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commit: 7079dcc

[greptile-apps]

Greptile Summary

This PR adds cd - style previous-account switching via codex-auth - and codex-auth switch -, backed by a new previous_active_account_key field persisted in the schema-4 registry. The implementation centralises state updates through a new setActiveAccountKey overload and a sibling setActiveAccountKeyPreservingPrevious function used in drift-correction and removal-replacement paths so that automatic registry syncs never clobber the user's explicitly recorded previous account.

• New SwitchTarget union replaces the flat query: ?[]u8 field in SwitchOptions, and the parser cleanly maps lone - at both the top-level and switch sub-command to .previous, rejecting flag combinations at parse time.
• Registry persistence adds previous_active_account_key to schema 4 (no version bump), and currentLayoutNeedsRewrite triggers a one-time normalisation rewrite for older schema-4 files that pre-date this field.
• Remove paths are updated to preserve the previous pointer when the removed account is not the recorded previous, and to clear it explicitly when it is.

Confidence Score: 5/5

Safe to merge — all three changed code paths (explicit switch, auto-replacement after remove, drift correction) consistently use the correct setter variant, and the one-time normalisation rewrite for existing schema-4 files terminates correctly after the field is written.

The centralisation of previous-account tracking in setActiveAccountKey is correct: same-account activations are a no-op for the previous field, drift-correction calls the Preserving variant so user-initiated history is never silently overwritten, and the removal path explicitly clears previous only when the removed account matches it. Memory ownership in handleSwitchPrevious is sound — the key is duped before activateAccountByKey frees the original through setActiveAccountKey. The schema normalisation trigger correctly distinguishes Zig null (key absent) from JSON null (key present-but-null), so subsequent loads do not re-trigger the rewrite. Test coverage is thorough, including the active==previous edge case after removal.

No files require special attention.

Important Files Changed

Filename	Overview
src/workflows/switch.zig	Refactored handleSwitch into three sub-functions (query/previous/picker); new handleSwitchPrevious correctly dupes the previous key before passing it to activateAccountByKey to avoid use-after-free.
src/registry/account_ops.zig	New setActiveAccountKey updates previous_active_account_key on every intentional switch; setActiveAccountKeyPreservingPrevious retained for drift-correction and removal-replacement paths; removeAccounts correctly clears previous only when the removed account matches it.
src/registry/storage.zig	currentLayoutNeedsRewrite correctly triggers a one-time normalisation rewrite for schema-4 files missing previous_active_account_key; JSON null vs Zig-null semantics handled correctly so the rewrite does not loop.
src/cli/commands/switch.zig	SwitchTarget union cleanly replaces the optional query field; lone - distinguished from flag prefixes; end-of-parse check rejects combinations with --live/--api/--skip-api.
src/workflows/active_auth.zig	reconcileActiveAuthAfterRemove now calls the Preserving variants so the user's recorded previous account is not overwritten by auto-replacement.
tests/cli_integration_test.zig	Comprehensive integration tests cover round-trip alternation, no-previous failure, missing-previous-account failure, active-removal replacement preserving previous, and active==previous edge case.
tests/registry_test.zig	Unit tests cover save/load round-trip, same-account idempotency, schema-4 normalisation rewrite, drift-correction preserving previous, and remove-clears-previous-key.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["CLI args parsed"] --> B{"opts.target"}
    B -- ".query" --> C["handleSwitchQuery"]
    B -- ".previous" --> D["handleSwitchPrevious"]
    B -- ".picker" --> E["picker / live flow"]
    D --> F{"previous_active_account_key?"}
    F -- "null" --> G["error: no previous account"]
    F -- "has key" --> H{"key in accounts list?"}
    H -- "no" --> I["error: previous account unavailable"]
    H -- "yes" --> J{"active == previous?"}
    J -- "yes" --> G
    J -- "no" --> K["activateAccountByKey -> setActiveAccountKey"]
    K --> L["saveRegistry -> printSwitchedAccount"]

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_{Reviews (3): Last reviewed commit: "fix: reject previous switch to active ac..." | Re-trigger Greptile}