fix(eap-items): Serialize EAPValue as untagged in attributes_array

[phacops]

Add #[serde(untagged)] to the EAPValue enum so that array attribute
values in attributes_array are serialized as plain values (e.g. 123,
"hello", 3.14, true) instead of tagged objects (e.g. {"Int": 123},
{"String": "hello"}).

The tagged representation included the enum variant name as a key, which
is not expected by downstream consumers that only need the raw values.

Agent transcript: https://claudescope.sentry.dev/share/Q6CFyxDoBsOrL1Z2w3da6gOTLnKW426exXCS65Bhk-Q

[sentry]

Bug: Adding #[serde(untagged)] to the EAPValue enum introduces a breaking serialization change, causing downstream Python consumers that expect a tagged object to crash with an AttributeError.
_{Severity: CRITICAL}

Suggested Fix

Either remove the #[serde(untagged)] attribute to revert to the previous tagged serialization format that downstream consumers expect, or update the Python consumer code (specifically the transform_array_value function) to correctly handle the new untagged primitive values.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent.
Verify if this is a real issue. If it is, propose a fix; if not, explain why it's not
valid.

Location: rust_snuba/src/processors/eap_items.rs#L177

Potential issue: The addition of `#[serde(untagged)]` to the `EAPValue` enum changes its
serialization format from a tagged object (e.g., `{"Int": 123}`) to a primitive value
(e.g., `123`). A downstream Python consumer, specifically the `transform_array_value`
function, expects the old tagged format and attempts to call `.items()` on each value.
When it receives a primitive type like an integer or string instead of a dictionary, the
call will fail with an `AttributeError`. This will cause runtime crashes in the
`get_trace` and `export_trace_items` RPC endpoints whenever they process items
containing array attributes.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.}

[cursor]

Backward incompatibility with existing tagged array data in storage

High Severity

The simplified process_arrays can no longer handle old tagged data already persisted in ClickHouse. Existing rows have array values in tagged format (e.g., {"Int": 123}), but the removed transform_array_value was the only code that unwrapped those dicts into plain values. Now, queries hitting old data will pass dict objects to _to_any_value or _value_to_attribute, which both raise BadSnubaRPCRequestException on the unhandled dict type. This will break reads until all old data expires per retention policy.

Additional Locations (1)

• rust_snuba/src/processors/eap_items.rs#L179-L180

 

[noahsmartin]

As long as no-one other than sessions is already using arrays, this looks great, thanks!

[onewland]

fine with this change but you should check that this doesn't break expectations for @thetruecpaul / @shashjar who I believe use arrays in occurrences today