docs: ADR-002 The Photon Token

docs/architecture/adr-002-photon-token.md

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+# ADR 002: The Photon token
+
+## Changelog
+
+- 15 October 2024: Initial version
+
+## Status
+
+DRAFT
+
+## Abstract
+
+This ADR proposes to introduce the PHOTON token (ticker `photon`) as the only
+fee token of AtomOne. The only way to get PHOTONs is to burn ATONEs.
+
+## Context
+
+The PHOTON token is specified in the [AtomOne Constitution Article 3 Section 5]:
+
+> ### Section 5: The PHOTON Token
+>
+> The PHOTON shall be the only fee token except for ATONE to PHOTON burn
+> transactions. This applies for all transactions on the root and core shards,
+> and all IBC and ICS payments.
+>
+> ATONE tokens may be burned to PHOTON tokens at a conversion rate set by law
+> such that the total amount of PHOTONs mintable through burning ATONE tokens
+> shall be capped at 1B PHOTON tokens.
+>
+> PHOTONs cannot be converted back into ATONE tokens.
+
+## Decision
+
+The ADR proposes to create a new `photon` module to host the following
+features:
+- New `ConversionRate` query
+- New `MsgBurn` message (XXX or `MsgMint`? or `MsgConvert` ? or something else?).
+- New [`TxFeeChecker`] implementation to enforce the PHOTON token as the only
+  fee token.
+
+### `ConversionRate` query
+
+The `ConversionRate` query returns a decimal which represents the current
+conversion rate of ATONE to PHOTON. This conversion rate is computed as the
+following:
+
+```math
+conversion\_rate = \dfrac{photon_{max\_supply} - photon_{supply}}{atone_{supply}}
+```
+where
+```math
+photon_{max\_supply} = 1,000,000,000
+```
+
+Given this formula, when the PHOTON supply reaches the max supply of 1 billion,
+it is no longer possible to get PHOTONs, because the conversion rate will return
+the 0 value.
+
+### `MsgBurn` message
+
+`MsgBurn` takes an amount of ATONEs and returns an amount of PHOTONs.
+The amount of ATONEs is burnt while the amount of PHOTONs is minted and moved
+onto the message signer account. The number of minted PHOTONs is equal to the
+number of burnt ATONEs multiplied by the conversion rate described in the
+`ConversionRate` query section below.
+
+```math
+photons_{minted} = atones_{burned} \times conversion\_rate
+```
+
+However, if `conversion_rate` is 0, i.e. the maximum supply of PHOTON has been
+reached, `MsgBurn` should fail to avoid burning ATONEs without PHOTONs in
+return.
+
+### `TxFeeChecker` implementation
+
+The [`TxFeeChecker`] is a function definition that is part of the ante handler
+`auth/ante.DeductFeeDecorator`. When this ante handler is invoked, it calls the
+`TxFeeChecker` to ensure that the fee specified in the tx is sufficient.
+
+Currently, AtomOne uses the default `TxFeeChecker` (namely
+[`checkTxFeeWithValidatorMinGasPrices`]), so the photon module must provide an
+alternative `TxFeeChecker` implementation, which should:
+- enforce that the fee denom is PHOTON, and return a specific error message if
+  it does not (this to be explicitely separated with the insufficient fee error
+  message)
+- make exception for some messages, specifically like `MsgBurn`, because
+  `MsgBurn` is the only way to get PHOTONs, so it should accept ATONEs as fee
+  token.
+
+### Params
+
+The `photon` module has the following params:
+- `mint_disabled` (default to false): if true, disable the ability to call
+  `MsgBurn`. 
+
+> [!NOTE]
+> XXX is it really usefull to disable `MsgBurn` ? Looks like it is an urgency
+> method when something goes wrong, which is not very compatible with a
+> governance proposal to change the parameters... Suggestion: remove it 
+
+> [!NOTE]
+> Because the maximum supply of PHOTON is constitutionnal, it must be hosted in
+> a constant in the code, and not in the parameters. (XXX true or not?)
+
+### State
+
+Aside from its params, the `photon` module does not have any additionnal state,
+as the PHOTON balances and supply are handled by the `bank` module.
+
+### Migration
+
+The PHOTON denom metadata has to be added to the `bank` module state (XXX while
+admittedly this record does not look very usefull, it is only used in
+queries...)
+
+```json
+{
+  "description": "The fee token of AtomOne Hub",
+  "denom_units": [
+    {
+      "denom": "uphoton",
+      "exponent": 0,
+      "aliases": [
+        "microphoton"
+      ]
+    },
+    {
+      "denom": "mphoton",
+      "exponent": 3,
+      "aliases": [
+        "milliphoton"
+      ]
+    },
+    {
+      "denom": "photon",
+      "exponent": 6,
+      "aliases": [
+        "photon"
+      ]
+    }
+  ],
+  "base": "uphoton",
+  "display": "photon",
+  "name": "AtomOne Photon",
+  "symbol": "PHOTON",
+  "uri": "",
+  "uri_hash": ""
+}
+```
+
+In contrast, it is not required to provide an initial supply for PHOTON (still
+in the `bank` module), because the initial supply will be 0.
+
+## Consequences
+
+### Validator `minimum-gas-prices`
+
+Validators will have to update their `minimum-gas-prices` setting to reflect
+this new setup. It should basically allow both ATONE and PHOTON, so the setting
+should look like:
+
+```toml
+minimum-gas-prices = "0.001uatone,0.001uphoton"
+```
+
+> [!IMPORTANT]
+> In the legacy `TxFeeChecker` implementation
+> ([`checkTxFeeWithValidatorMinGasPrices`]), the validator `minimum-gas-prices`
+> is checked against *all* mentionned denoms. For the photon module, the
+> implementation must be different, it must be checked on at least one of the
+> denoms (ATONE or PHOTON, but not both).
+
+If the validator `minimum-gas-prices` does not match the required denom (ATONE
+or PHOTON for `MsgBurn, only `PHOTON` for all other messages), an error is
+returned and the tx is rejected.
+
+### Positive
+
+- Create a clear distinction between money (PHOTON) and security (ATONE). ATONE
+  is not money and should only be thought of as a security token. PHOTON as the
+  only fee token reinforces this property.
+
+- Having a non-inflationnary fee token (in contrast to ATONE) ensures PHOTON
+  will continue to gain value in line with AtomOne usage. The more
+  transactions there are, the more PHOTON is needed, bringing scarcity and
+  value.
+
+- The requirement of burning ATONE to get PHOTON also has the side effect of
+  bringing more value to ATONE, thanks to the decrease of the total supply of
+  ATONE that happens in the process.
+
+### Negative
+
+- Users will have to choose between PHOTON and ATONE for the fee token when
+  signing a transaction for AtomOne. Basically, for `MsgBurn` ATONE and PHOTON
+  are accepted, for all other messages, only PHOTON is accepted. While this
+  may seem obvious, it can be confusing because as far as we know, wallets do
+  not have message-based logic regarding the choice of the fee token. Maybe it
+  is time to start discussion with some wallets dev regarding that, this would
+  improve the UX.
+
+> [!NOTE]
+> XXX [`TxFeeChecker`] allows to override the tx fee, one solution for the
+> problem above is to override the tx fee denom with PHOTON and keep the
+> amount. Note sure this is a good way though, sounds weird to accept a tx and
+> deduct from the tx signer balance a different denom than the one specified.
+
+### Neutral
+
+- Dual token model like this has not been experimented at this scale in the
+  Cosmos ecosytem, we might experience some unexpected side effect, positive or
+  negative.
+
+## References
+
+* [AtomOne Constitution Article 3 Section 5]: The PHOTON Token
+
+[AtomOne Constitution Article 3 Section 5]: https://github.com/atomone-hub/genesis/blob/b84df30364674c3f68b4bc0a43d7ed977ae22226/CONSTITUTION.md#section-5-the-photon-token
+[`TxFeeChecker`]: https://github.com/cosmos/cosmos-sdk/blob/44c5d17ca6d9d37fdd6adfa3169c986fbce22b8f/x/auth/ante/fee.go#L11-L13
+[`checkTxFeeWithValidatorMinGasPrices`]: https://github.com/cosmos/cosmos-sdk/blob/6e59ad0deea672a21e64fdc83939ca812dcd2b1b/x/auth/ante/validator_tx_fee.go#L17

docs/architecture/adr-template.md

@@ -1,58 +1,58 @@
-<!--
-order: false
--->
-
-# ADR {ADR-NUMBER}: {TITLE}
-
-## Changelog
-
-- {date}: {changelog}
-
-## Status
-
-{DRAFT | PROPOSED} Not Implemented
-
-> Please have a look at the [PROCESS](./PROCESS.md#adr-status) page.
-> Use DRAFT if the ADR is in a draft stage (draft PR) or PROPOSED if it's in review.
-
-## Abstract
-
-> "If you can't explain it simply, you don't understand it well enough." Provide
-> a simplified and layman-accessible explanation of the ADR.
-> A short (~200 word) description of the issue being addressed.
-
-## Context
-
-> This section contains all the context one needs to understand the current state, and why there is a problem. 
-> It should be as succinct as possible and introduce the high level idea behind the solution. 
-> The language in this section is value-neutral. It is simply describing facts.
-
-## Decision
-
-> This section explains all of the details of the proposed solution, including implementation details.
-It should also describe affects / corollary items that may need to be changed as a part of this.
-If the proposed change will be large, please also indicate a way to do the change to maximize ease of review.
-(e.g. the optimal split of things to do between separate PR's)
-
-## Consequences
-
-> This section describes the consequences, after applying the decision. 
-> All consequences should be summarized here, not just the "positive" ones.
-
-### Positive
-
-> {positive consequences}
-
-### Negative
-
-> {negative consequences}
-
-### Neutral
-
-> {neutral consequences}
-
-## References
-
-> Are there any relevant PR comments, issues that led up to this, or articles referrenced for why we made the given design choice? If so link them here!
-
-* {reference link}
+<!--
+order: false
+-->
+
+# ADR {ADR-NUMBER}: {TITLE}
+
+## Changelog
+
+- {date}: {changelog}
+
+## Status
+
+{DRAFT | PROPOSED} Not Implemented
+
+> Please have a look at the [PROCESS](./PROCESS.md#adr-status) page.
+> Use DRAFT if the ADR is in a draft stage (draft PR) or PROPOSED if it's in review.
+
+## Abstract
+
+> "If you can't explain it simply, you don't understand it well enough." Provide
+> a simplified and layman-accessible explanation of the ADR.
+> A short (~200 word) description of the issue being addressed.
+
+## Context
+
+> This section contains all the context one needs to understand the current state, and why there is a problem. 
+> It should be as succinct as possible and introduce the high level idea behind the solution. 
+> The language in this section is value-neutral. It is simply describing facts.
+
+## Decision
+
+> This section explains all of the details of the proposed solution, including implementation details.
+It should also describe affects / corollary items that may need to be changed as a part of this.
+If the proposed change will be large, please also indicate a way to do the change to maximize ease of review.
+(e.g. the optimal split of things to do between separate PR's)
+
+## Consequences
+
+> This section describes the consequences, after applying the decision. 
+> All consequences should be summarized here, not just the "positive" ones.
+
+### Positive
+
+> {positive consequences}
+
+### Negative
+
+> {negative consequences}
+
+### Neutral
+
+> {neutral consequences}
+
+## References
+
+> Are there any relevant PR comments, issues that led up to this, or articles referrenced for why we made the given design choice? If so link them here!
+
+* {reference link}