feat(safety): freeze/unfreeze kill switch, init→setup-policy chain, spend line

[SELAT-DEV]

Summary

Tester feedback WS4 remainder, layered on the merged session-budget chain (#68). Pairs with selat-pay feat/freeze (#23), which enforces the flag pre-signature.

selat freeze / selat unfreeze — instant local kill switch

• selat freeze [--note "<why>"] writes the flag file ($XDG_STATE_HOME/selat-pay/frozen.json, SELAT_PAY_FREEZE_PATH override; schema owner is selat-pay); every paid call is refused before signing until selat unfreeze removes it. Local and instant — no Circle round-trip. Probes and free discovery keep working.
• selat budget shows the FROZEN state prominently while active — first line of the human display (bold red), plus a frozen field and prefixed user_summary in --json.
• Wired into bin/selat.mjs + top-level help; both commands have --help.

selat init → setup-policy chaining

At the end of init's success path, when the wallet has no custom spending policy (best-effort spendingPolicy() read — an unreadable policy stays silent instead of nagging on a Circle hiccup): a strong recommendation block, then

• interactive stdin: promptYesNo "Set spending caps now?" (default YES) → runs the existing setup-policy flow (Circle's pattern: the email-OTP prompt belongs to the user's own terminal, inherit: true)
• non-TTY: prints the verbatim selat setup-policy command instead of hanging on a prompt

The closing "Set a spending policy before depositing > $20" hint is skipped when caps exist or were just set.

Confirmation-time spend line

When a session budget is armed, the moment money is about to move now shows session: $X spent of $Y:

• selat run pre-payment output (non-json) — both the x402 path and the Apify prepaid-token path
• selat fund's plan block (aligned as a plan row)

Reuses budget.mjs's readSessionConfig/sessionSpent via a new exported sessionSpendLine() helper.

Tests

• New test/freeze-and-policy-chain.test.mjs: freezeFilePath/readFreeze (fail closed on malformed flag)/freezeStatusLine/noteArg, the freeze/unfreeze commands against a temp flag path (0600, schema, re-freeze refresh, idempotent unfreeze), policyChainDecision (prompt / print / silent-when-capped / silent-when-unreadable), and sessionSpendLine
• Full suite: 112/112 pass (was 105 on main); npm run check clean

Live verification (no money moved)

Drove bin/selat.mjs with fake XDG_*/SELAT_PAY_* paths, a stub CIRCLE_BIN, and an armed fake session ledger: freeze --note → flag written (schema v1) → budget shows the FROZEN line + session $0.0150 spent of $2 → --json carries frozen → unfreeze removes the flag. Cross-repo: the flag written by selat freeze trips selat-pay's enforceNotFrozen() with the exact refusal message, and reads null after selat unfreeze.

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