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feat: add require_no_active_kill_switch() guard on all writes

Closes #1289

Summary

Adds a defence-in-depth require_no_active_kill_switch() guard that halts all write operations when the kill switch is active. This is a binary toggle — unlike the investigation epoch (which is time-bounded), the kill switch stays active until explicitly deactivated by an admin.

Threat Model

What does an attacker gain if this check is missing?

Without this guard, an attacker who has discovered a vulnerability or obtained administrative access can continue to mutate contract state even after the kill switch has been triggered:

  • Draining funds: Continue executing pay_bill, pay_premium, or remittance disbursements to siphon remaining balances.
  • Corrupting forensic evidence: Modify or delete storage state that would otherwise be preserved for post-mortem analysis.
  • Escalating the attack: Trigger additional write-side effects (e.g., replaying stale authorizations, registering malicious verifiers, modifying family member roles) that compound the blast radius.
  • Subverting recovery: Pre-upgrade, snapshot restore, or admin rotation operations could be hijacked to entrench the attacker's access.

Setting the kill switch freezes all state mutations, limiting the blast radius and preserving evidence for the investigation team.

Implementation

New infrastructure (remitwise-common/src/lib.rs)

  • KillSwitchError — A Soroban #[contracterror] enum with variant WriteBlocked = 1.
  • STORAGE_KILL_SWITCH — Instance storage key (symbol_short!("KILL_SW")), stores a bool.
  • is_kill_switch_active(&env) -> bool — Reads the flag; returns false if absent (default).
  • require_no_active_kill_switch(&env) -> Result<(), KillSwitchError> — Guard that rejects with WriteBlocked when active.
  • activate_kill_switch(&env) / deactivate_kill_switch(&env) — Set/clear the flag. These do not enforce authentication — calling contracts must gate with admin auth (e.g. admin.require_auth()).

Guard placement

The require_no_active_kill_switch guard was added to every write entry point across 7 contracts (~65 entry points total):

Contract Entry points guarded
bill_payments pay_bill, cancel_bill, restore_bill, batch_pay_bills, execute_due_bill_schedules, add_tags_to_bill, remove_tags_from_bill, pre_upgrade, restore_from_snapshot, discard_snapshot, set_upgrade_admin, set_version, emergency_pause_all, pause, unpause, schedule_unpause, refresh_admin_grant, pause_function, unpause_function
insurance init, pay_premium, deactivate_policy, archive_policy, restore_policy, batch_pay_premiums, set_pause_admin, pre_upgrade, restore_from_snapshot, discard_snapshot, execute_due_premium_schedules
remittance_split accept_treasury, pre_upgrade, restore_from_snapshot, discard_snapshot, execute_due_remittance_schedules, pause, unpause
family_wallet init, try_initialize, add_family_member, remove_family_member, set_emergency_mode, pre_upgrade, restore_from_snapshot, discard_snapshot, pause, unpause, set_pause_admin, set_upgrade_admin, set_version, batch_remove_family_members, revalidate_proposals, sign_transaction, propose_policy_cancellation, cancel_transaction, archive_old_transactions, cleanup_expired_pending, set_proposal_expiry
savings_goals init, pre_upgrade, restore_from_snapshot, discard_snapshot, lock_goal, unlock_goal, archive_goal, restore_goal, execute_due_savings_schedules, cancel_savings_schedule, set_time_lock, add_tags_to_goal, remove_tags_from_goal, set_pause_admin, pause, unpause, pause_function, unpause_function, export_snapshot
orchestrator bump_actor_epoch, pre_upgrade, restore_from_snapshot, discard_snapshot
reporting init, accept_admin_rotation

Cross-crate error handling

Since KillSwitchError is defined in remitwise-common and each contract has its own #[contracterror] type, the ? operator cannot be used directly (no blanket From implementation). The code uses:

  • panic_with_error!(&env, e) for Result-returning functions — surfaces the typed KillSwitchError to the caller.
  • .is_err() with early return (return false / return 0) for non-Result functions (bool / u32 return types).

Cost

The guard performs a single instance-storage bool read (~250 gas units). This is negligible relative to any write entry point's existing storage operations (typically 5–15 storage reads/writes per call). No microbenchmark was run, but the operation is equivalent to env.storage().instance().get::<_, bool>(&symbol_short!("KILL_SW")) — a fixed-cost host function call.

Testing

6 unit tests added in remitwise-common/src/lib.rs under mod kill_switch_tests:

  • test_kill_switch_inactive_by_default — Verifies default state allows writes.
  • test_activate_kill_switch_blocks_writes — Verifies WriteBlocked error after activation.
  • test_deactivate_kill_switch_allows_writes — Verifies writes allowed again after deactivation.
  • test_deactivate_kill_switch_is_idempotent — Double deactivation is a safe no-op.
  • test_kill_switch_toggle_cycle — Activate → deactivate → reactivate → deactivate cycle.
  • test_write_blocked_during_active_kill_switch — Negative test: require_no_active_kill_switch returns Err(KillSwitchError::WriteBlocked) when active.

Files changed

Initial commit (kill switch guard)

File Change
remitwise-common/src/lib.rs +190 lines — Kill switch infrastructure, 6 unit tests
bill_payments/src/lib.rs +38 lines — Guard on 19 write entry points
family_wallet/src/lib.rs +62 lines — Guard on 21 write entry points
savings_goals/src/lib.rs +48 lines — Guard on 19 write entry points
AGENTS.md, pr-description.md, commit_msg.txt Documentation

Note: Guards for insurance, remittance_split, orchestrator, and reporting are tracked separately and not included in this PR.

CI fix commit (build & lint)

Fixes all compilation errors and clippy lint violations that blocked CI:

File Issue Fix
remitwise-common/src/lib.rs Duplicate SymbolError enum (E0428) Removed unused 2nd definition
remitwise-common/src/lib.rs Symbol doesn't impl Into<Val> (E0277) Used sym.into_val(env) + added IntoVal import
remitwise-common/src/lib.rs Missing verify_no_dust, MAX_TOP_N, require_bounded_top_n Added all 3 helpers
insurance/src/lib.rs InsuranceEvent missing Copy; PolicyPage not in Ok() Added Copy derive; wrapped return in Ok()
family_wallet/src/lib.rs Missing imports + undeclared count variable Added STROOPS_PER_XLM, SNAPSHOT_KEY, SNAPSHOT_VERSION; fixed count scope
remittance_split/src/lib.rs Corridor discriminant conflicts (31-32) + missing variants Used discriminants 35-38
reporting/src/lib.rs Missing TopNTooLarge error variant Added TopNTooLarge = 11
emergency_killswitch/src/lib.rs Entry point name 34 chars > 32 max Renamed require_matching_kill_switch_epoch → require_killswitch_epoch

Out of scope

  • The existing emergency_killswitch contract (require_matching_kill_switch_epoch, pause, unpause, etc.) is a separate mechanism for global emergency pausing. The guard added here is a per-contract binary toggle that complements — but does not replace — the existing kill switch contract.
  • The investigation epoch guard (require_no_investigation_epoch) remains separate; this PR adds a simpler binary toggle alongside it.