imp

# Imp v0.16.1

Imp is a framework for typed, optimizable language-model programs on the BEAM.
This release fixes how ReActV2 replays a history turn that a host stored with
the task's inputs and its answer, and no step of the loop's own. Under
`finish: :submit` and `finish: :tools`, since 0.14.0, such a turn replayed only
its inputs: the model read the event and not the answer stored with it. It now
replays as the model's message holding that answer, as it always has under
`finish: :auto`. It adds no options and changes no public API, so under Imp's
versioning rule this is a patch release.

## Install

```elixir
{:imp, "~> 0.16.0"}
```

`~> 0.16.0` takes later 0.16 patch releases and nothing newer. The two-part
form, `~> 0.16`, means `>= 0.16.0 and < 1.0.0` in Mix, so `mix deps.update
imp` under it takes every later 0.x release, including minor releases that
change what callers receive.

Every dependency comes from Hex. Use a path dependency only while developing
against a local checkout.

ExMCP and erlexec are declared `runtime: false`, so an OTP release that uses
`Imp.ACP` or `Imp.MCP` must list `applications: [ex_mcp: :load, erlexec: :load]`
in its release definition; see [releases that use MCP or
ACP](docs/production.md#releases-that-use-mcp-or-acp).
Ordinary Imp startup starts no protocol endpoint.

## Changes and upgrading from 0.16.0

Under `{:imp, "~> 0.16.0"}`, run `mix deps.update imp` and commit `mix.lock`.
No code or data migration is needed.

- **Fixed: a stored answer turn replays its answer under every ending.**
  ReActV2 reads a stored turn that carries the inputs and the one output of
  the task, and neither `next_thought` nor `tool_calls`, as a step that
  answered in text. Since 0.14.0 it did so only when the program ended in
  plain text (`finish: :auto`); under `finish: :submit` and `:tools`, with
  either `history_replay`, the request held the turn's inputs as a user
  message and no assistant message after them. A host that writes such a
  turn, for example a recap standing in for the earlier conversation, had
  its content left out of every request. The turn now replays as one
  assistant message holding the answer, with no "not sent" line after it,
  since it carries the task's output. Turns the loop writes itself are
  unchanged, and the history the caller holds is unchanged. Under
  `finish: :auto`, a one-output signature whose output is constrained or not
  typed string gets the same replay when the stored value is a string.

Rollback means restoring `0.16.0` in the lock; such turns then replay their
inputs alone again under `finish: :submit` and `:tools`. See the
[changelog](CHANGELOG.md) for every change.

## Known limits

- The usage map (`:usage` on the `:model_response` event, `Imp.Usage`,
  `Imp.Prediction.get_lm_usage/1`) is ReqLLM's, with `input_includes_cached`
  added. Its `:cost` and `:total_cost` are ReqLLM's catalog estimate, not a
  charge, for streamed and non-streamed calls alike, and OpenRouter's charge
  is its `"cost"`.
  Read money from `cost` and `estimated_cost`.
- An error the provider sends inside a stream has `status` `nil` and
  `retryable: true`, because ReqLLM's stream decoder keeps only its message;
  the same error in a non-streamed response may carry a status that says not
  to retry.
- A flat two-element name-first list that is not itself an element of a
  list (at the top level, in a tuple, or under a key that is not a credential
  name), such as `["password", "hunter2"]`, is not redacted, where 0.5.0
  redacted it. Such a list is read as a key and value only as an element of a
  list, so that lists of names such as `with_inputs([:api_key, :question])`
  survive saving.
- The GEPA, SIMBA, MIPROv2, InferRules and random-search checkpoints redact
  their failure reasons but otherwise hold the resume state as it is: GEPA's
  candidates, evaluation cache, proposed instructions and reflection data, and
  the others' instructions, demos and scores. Fast-Slow and Playbook
  checkpoints likewise hold their prompts, rollouts and playbooks. Treat
  checkpoint files as sensitive.
- A ReActV2 step whose prose quotes its own field names (a JSON object with
  `next_thought` or `tool_calls` keys, a `[[ ## field ## ]]` line, a
  `<next_thought>` tag) is not read as prose and goes to the JSON fallback,
  which usually costs one more call. If the model repeats the same reply, the
  step ends `:incomplete`. Beside native tool calls, such a thought becomes
  `nil`; the calls still run.
- Tool images reach the model as user messages after the turn's tool
  responses, labelled with the call, not nested in the tool result, even for
  providers that accept images in tool results. Only MCP text and image
  blocks are converted; other block types stay text, image URLs in text are
  never fetched, and the selected model must accept image input of that
  format and size.
- ATIF's `extra.seen_by_model` and the read-as `content` come from matching
  a tool message in the next captured request. A result that request does
  not carry, including one that ended the run, keeps the tool's own output
  and is marked unseen. `agent.tool_definitions` comes only from `:tools_sent`
  events, and `final_metrics` totals are left out when any response lacks
  that figure.
- A streamed completion that the provider's content filter stops still ends
  as a completion: the stream's `finish_reason` is `:content_filter` and the
  filter's text has already arrived as chunks. Only non-streamed requests
  turn it into an `Imp.LMError`.
- When a streamed ReqLLM request fails, ReqLLM's own warning log prints the
  error with its response headers. Imp strips them from the error it returns,
  but cannot change that log line.
- In command output, a `Bearer` token of 12 to 15 characters, or one with no
  digit, is shown when more text or a newline follows it. 0.5.0's command
  pipeline hid any such token of 12 or more characters.
- A GEPA checkpoint taken between preparing and starting a full validation
  resumes by rejecting that candidate, as before.

The [CHANGELOG](CHANGELOG.md) records every user-visible change in this
release. Generated module documentation is the complete API reference. Start
with `Imp`, `Imp.Signature`, `Imp.Module`, `Imp.Evaluate`, `Imp.Optimizer`,
`Imp.ACP`, `Imp.MCP`, and `Imp.Telemetry`.