Migrate money surfaces from karma to credits (content-server #2086 / W5.3)

[baoinf]

Tracks the SDK-side migration for content-server #2086 (W5.3).

Context

content-server #2086 changes every agent-facing REST response and usage header to present money as USD-denominated credits instead of karma, using the canonical rate 1 credit = $1.00 = 1,000 karma (credits = karma / 1000, 4dp).

Per the decision on that issue, this is a replace, not additive change: the karma_* fields and X-*-Karma-* headers are removed and replaced with credit equivalents — there is no one-release deprecation window. That makes it a breaking change for this SDK, which is why it needs its own tracked migration that lands after content-server #2086 deploys.

Two things change on the wire:

1. Field/header renames — karma_* → credits_* (e.g. karma_charged → credits_charged, karma_cost → credits_cost, amount_karma → amount_credits, estimated_karma_cost → estimated_credits_cost); currency on the credits endpoint becomes "credits"; headers X-Karma-Used/Balance → X-Credits-Used/Balance and X-Deva-Karma-Cost/Balance → X-Deva-Credits-Cost/Balance.
2. Magnitude + type change — every money value shrinks by a factor of 1,000 and goes from an integer karma count to a 4dp credit decimal (e.g. balance 1000 → 1.0000, a 58-karma image cost → 0.0580).

Internal karma logic on the server (charging, buckets, ledger, emission) is unchanged — only the presented unit changes.

SDK touch-points to update

Audit of src/ against the credits-only surface:

• src/types.ts:149 — chat usage object deva?: { karma_cost; karma_balance } → { credits_cost; credits_balance }; update any header parsing that reads X-Deva-Karma-Cost / X-Deva-Karma-Balance to the X-Deva-Credits-* names.
• src/resources/wallet.ts:5 — WalletBalance.karma?: number → credits (decimal); revisit available / pending if they are karma-denominated.
• src/resources/models.ts:6-9 — prompt_karma / completion_karma per-token pricing and currency — confirm whether these are sourced from a content-server surface in scope of #2086; migrate to credit-denominated pricing if so.
• src/errors.ts:45 — "Out of karma / quota" comment; reword to credits (cosmetic).
• Sweep examples/ and README.md for karma-denominated numbers and 1000 karma = $1 framing; restate as credits.
• Bump SDK version and note the breaking change in the changelog once content-server #2086 is live.

Coordination

• Land and release after content-server #2086 is deployed to production (the wire format flips at that point).
• No dual-read/back-compat path is needed on the server side, so pin the minimum server version this SDK release targets.

Out of scope

• Any change to how karma is charged or accounted on the server (unchanged — presentation only).
• Deva-social user-facing karma.