Previous logic (LLM summary):
> The current logic always prefers captured over outcome, even when outcome is an Err. Consider: callback runs successfully → slot = Some(Ok(value)) → returns None → but then runInteraction's commit fails and the deferred errbacks. Now captured = Some(Ok(value)) and outcome = Err(...), and we'd return Ok(value) — silently swallowing the commit failure.
>
> Whether that's reachable depends on Synapse's retry behavior (it may retry the whole interaction on commit failure, re-running the callback). It's likely a narrow edge case, but the comment ("we only trust this slot once the deferred has fired") implies the slot is authoritative once fired, which isn't quite true if the deferred fires with an error after a successful callback run.
LLM summary:
func only ever needs to be moved to a thread and called there sequentially, never shared by & across threads:
- In the erasure, func is captured by-move into the Box<dyn Fn ... + Send> callback (only Send is required to box it that way).
- The Python pool moves that callback into the runInteraction DB-thread closure and calls it there; the Rust pool calls it within a single async task. Neither sends &func to multiple threads concurrently.
Prompt:
```
Compare this with a previous approach that was swapped out in `d9a111bdfaf51cd4cadfdc071f9956eec47aea43` (look at the removals). Anything we should change/simplify or something you like better/worse about that one? Give the new approach a review and simplify and make things more clear as necessary
```
Changes made (LLM summary):
1. #[async_trait] on the object-safe method. The core trait method is now async fn run_interaction_erased(...) -> ErasedResult instead of a hand-rolled fn ... -> BoxFuture<'a, _>. This is the convention already used by Transaction in the same file, and it removed the async move { ... }.boxed() wrapper (plus the BoxFuture/FutureExt imports) from both pool impls — their bodies are now plain async fns again.
2. Dropped the constrain / erase_interaction helper. I'd over-engineered the closure erasure out of a worry that higher-ranked-lifetime inference would fail. The previous code proved a direct let erased: ErasedInteraction = Box::new(move |txn| {...}) compiles — the type annotation on the binding is enough. ~30 lines gone.
3. Dropped the unneeded + Sync on the erased callback type. ErasedInteraction is + Send only now; the boxed callback is moved to a single DB thread and called there, never shared by reference.
```
[ERROR]
Traceback (most recent call last):
File "/home/eric/.cache/pypoetry/virtualenvs/matrix-synapse-xCtC9ulO-py3.14/lib/python3.14/site-packages/twisted/trial/runner.py", line 711, in loadByName
return self.suiteFactory([self.findByName(name, recurse=recurse)])
File "/home/eric/.cache/pypoetry/virtualenvs/matrix-synapse-xCtC9ulO-py3.14/lib/python3.14/site-packages/twisted/trial/runner.py", line 474, in findByName
obj = reflect.namedModule(searchName)
File "/home/eric/.cache/pypoetry/virtualenvs/matrix-synapse-xCtC9ulO-py3.14/lib/python3.14/site-packages/twisted/python/reflect.py", line 156, in namedModule
topLevel = __import__(name)
File "/home/eric/Documents/github/element/synapse/tests/__init__.py", line 24, in <module>
from synapse.util.patch_inline_callbacks import do_patch
File "/home/eric/Documents/github/element/synapse/synapse/__init__.py", line 31, in <module>
from synapse.util.rust import check_rust_lib_up_to_date
File "/home/eric/Documents/github/element/synapse/synapse/util/__init__.py", line 41, in <module>
from synapse.types import JsonDict
File "/home/eric/Documents/github/element/synapse/synapse/types/__init__.py", line 63, in <module>
from synapse.api.errors import Codes, SynapseError
File "/home/eric/Documents/github/element/synapse/synapse/api/errors.py", line 33, in <module>
from synapse.util.json import json_decoder
File "/home/eric/Documents/github/element/synapse/synapse/util/json.py", line 23, in <module>
from synapse.synapse_rust.events import JsonObject
File "/home/eric/Documents/github/element/synapse/synapse/logging/context.py", line 55, in <module>
from synapse.util.stringutils import random_string_insecure_fast
File "/home/eric/Documents/github/element/synapse/synapse/util/stringutils.py", line 31, in <module>
from synapse.api.errors import Codes, SynapseError
builtins.ImportError: cannot import name 'Codes' from partially initialized module 'synapse.api.errors' (most likely due to a circular import) (/home/eric/Documents/github/element/synapse/synapse/api/errors.py)
```
This is in prep for converting the event serialization to Rust.
This is a fairly mechanical port, except that we store the appservice ID
rather than the appservice object. This avoids us having to store a
`Py<..>` (or port the appservice object over).
Follow on from #19701
This (more or less) matches what we had before. Otherwise we just get a
default `<builtins.Event at 0x...>`
---------
Co-authored-by: Eric Eastwood <erice@element.io>
Follow on from https://github.com/element-hq/synapse/pull/19701.
Unfortunately serde has a bug when using `#[serde(flatten)]` with
`arbitrary-precision` feature when handling integers that fit in a i128
when doing `serde_json::from_value`. See
https://github.com/serde-rs/serde/issues/2230.
The `depythonize` hits the same issue. To fix this we make it so we only
parse events from strings and not values.
Eric Eastwood