Document new miner needing positive balance to pay for fees before they start winning block rewards

[BigLep]

@irenegia is going to put together some numbers for this to illustrate the costs and timing involved. You need 10TiB of RBP to start winning block rewards, so your miner needs to be funded to pay the fees for this.

See also this thread: filecoin-project/FIPs#1105 (reply in thread)

Discussion thread has been updated by Irene and Beck, there are some good figures and discussion points in there about the amount a miner actor should have available before they start winning block rewards to cover the fees. It's not huge but it's important to make new SPs aware that when making a miner actor and onboarding sectors that they should have a non-zero balance with enough to cover fees until they start collecting block rewards. You become eligible at 10TiB but may not start winning until later thanks to randomness and the number of competing miners.

@TippyFlitsUK & @rjan90 I put you down as owners of this issue, do we have a good place where we discuss such things in our documentation where this could be added?

Slack thread: https://filecoinproject.slack.com/archives/C06AM5STJ8K/p1743481224463389?thread_ts=1743073205.101329&cid=C06AM5STJ8K

For visibility, here is text from the slack thread:

Relevant info from slack messages:

Currently, in order to avoid the FeeDebt situation and be eligible for block production, a miner needs to have in its balance enough tokens to pay for gas fees for windowPoSt (to avoid losing power and having to pay the fault fee).
After nv25 (because of FIP0100), they also need to account for the new daily fee. Indeed, tokens in the locked vesting may not be enough to cover for the new fee, especially for small miners.

When is the fee taken?

• At the end of each deadline (except the sector’s final deadline before expiry). Fees start accruing the day after a sector is committed or extended (unless in grace period)

How is the fee paid?

• The SP doesn't manually send a message. The mechanism first tries to deduct the fee from future vesting rewards. If those aren’t sufficient, it falls back to deducting from the miner’s balance. If there are still not enough funds, the miner accrues fee debt.

Does fee debt cause sector faults?

• No, fee debt by itself does not cause sector faults, but having high fee debt might increase your risk of falling into faults indirectly because:
  • The system could draw down your miner balance trying to cover the debt.
  • If your balance drops too low, and you don’t have enough FIL to cover window PoSt fees.

How can I best plan to avoid Fee Debt?

• Maintain a buffer in your miner's balance to prevent fee debt.
• Avoid withdrawing all unlocked funds unless you're sure future rewards will cover the fees.

What is the grace period?

• There’s a 90-day grace period from FIP activation. During this time, extensions of pre-FIP sectors do not trigger the daily fee. Snaps do trigger the fee immediately, even during the grace period.

[BigLep]

Per 2025-05-07 FilOz weekly meeting, it was agreed that @TippyFlitsUK will take this, ideally adding content in or around https://github.com/filecoin-project/filecoin-docs/blob/main/storage-providers/basics/README.md

[TippyFlitsUK]

Added here #2396