Auto-allocate default_credit on user create / update

Credit behavior on POST /api/v1/auth/users and PUT /api/v1/auth/users/{user_id}.

User create/update still succeeds when auth checks pass. Credit allocation is soft-fail: missing or insufficient budget does not fail the user API.

Helpers live in app/features/rate_limit/service.py:

• delete_user_credit_config — removes UserLlmCreditConfig (no used guard)
• try_allocate_default_user_credit — allocates org default_credit when possible; notifies the requester on budget / usage shortfall

Available budget:

remaining = org.limit_credits - SUM(user_llm_credit_configs.limit_credits)

Allocate only when all of:

• target user is not system_admin (quota bypass)
• org has OrgLlmCreditConfig and default_credit > 0
• user has no existing UserLlmCreditConfig
• remaining >= default_credit
• current-period used <= default_credit

Notify type: llm_credit_org_budget_insufficient (requester only).

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Create user (POST /auth/users)

#	Condition	Credit behavior	Notify requester?
C1	New user, has org_id, default_credit > 0, remaining OK, used OK	Create UserLlmCreditConfig with limit = default_credit	No
C2	Has org_id, default_credit > 0, remaining < default_credit	No config	Yes
C3	Has org_id, default_credit > 0, used > default_credit	No config	Yes
C4	default_credit = 0 or no OrgLlmCreditConfig	No config	No
C5	org_id is None	Skip allocate	No
C6	Target is system_admin	Skip (quota bypass)	No

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Reactivate user (same POST, soft-deleted email)

When create finds an existing user with deleted=True, it reactivates that row (same user_id) instead of inserting a new user.

#	Condition	Credit behavior	Notify?
R1	Org changed + old config exists	Delete old config → try allocate for new org (C1–C6)	Only if allocate fails (budget / used)
R2	Same org + config already exists	No delete; allocate no-op	No
R3	Same org + no config yet	Try allocate like create	Same as C1–C3

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Update user (PUT /auth/users/{id}, admin path)

Self-edit by a non–system_admin returns early and does not touch credit (U7).

#	Condition	Credit behavior	Notify?
U1	Org changed + old config exists	Delete old config → allocate for new org	Only if allocate fails
U2	Org changed + no config	Allocate for new org	Same as above
U3	Org changed → org_id = null (sysadmin)	Delete old config; no allocate	No
U4	Same org + no config + default_credit > 0 + budget OK	Backfill: create config	No
U5	Same org + no config + insufficient budget / used	No config	Yes
U6	Same org + config already exists	Allocate no-op (keep old limit)	No
U7	Self-edit (non–sysadmin edits self)	Early return — no credit logic	No

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Quick summary

Action	When config is created	When config is deleted	When requester is notified
Create	Budget + default OK	—	Allocate attempted but remaining/used blocks it
Reactivate org change	After delete, if new org OK	Always if old config exists	Same as create shortfall
Update org change	After delete, if new org OK	Always if old config exists	Same
Update same org, no quota	Backfill if OK	—	Shortfall only
Update same org, has quota	—	—	—