# ms.1 — Pipeline anyhow-chain preservation — Implementation Plan

> **Parent spec:** `docs/specs/0018-multi-subject-codellama.md`
>
> **For agentic workers:** REQUIRED SUB-SKILL: use `skills/implement`
> to run this plan. Steps use `- [ ]` checkboxes for tracking.

**Goal:** Fix the JSON-cohort feedback bug where harness-side
`module_name_from_json` failures lose their `Caused by:` chain on
the way into the model prompt. Change is two characters, gated by a
RED→GREEN unit test.

**Architecture:** `pipeline.rs:118` formats an `anyhow::Error` with
`{e}` (Display), which prints only the top-level message. The
underlying serde-parse-error sits in the cause chain and is
dropped. Switch to `{e:#}` (alternate Display), which joins the
chain with `: ` separators on a single line — survives the
existing `strip_locations` regex (which only collapses `\nCaused
by:` blocks, not `: `-joined chains) and lands a fully informative
diagnostic in the model's next-turn prompt.

**Tech Stack:** Rust 1.x, `anyhow`, `serde_json`,
`xmodel_harness::pipeline`.

**Files this plan creates or modifies:**

- Modify: `experiments/2026-05-12-cross-model-authoring/harness/src/pipeline.rs:118` — change `format!("check: {e}")` to `format!("check: {e:#}")`
- Modify: `experiments/2026-05-12-cross-model-authoring/harness/src/pipeline.rs` — add (or extend if present) `#[cfg(test)] mod tests` block with the RED→GREEN test

**Recon note (Boss-direct, no agent dispatch):** the iter touches
one file at one line; the Boss verified the current source verbatim
during the brainstorm session (see iter journal). `ailang-plan-recon`
dispatch skipped — context already loaded.

---

## Task 1: RED test — anyhow chain preservation

**Files:**
- Modify: `experiments/2026-05-12-cross-model-authoring/harness/src/pipeline.rs` — add `#[cfg(test)] mod tests` if not present, or extend if present

- [ ] **Step 1: Add the failing test**

At the bottom of `pipeline.rs`, add:

```rust
#[cfg(test)]
mod tests {
    use anyhow::{anyhow, Context, Error};

    /// Constructs the same chain shape `module_name_from_json`
    /// produces on a serde-parse failure: a leaf error wrapped
    /// with a "parsing JSON in <path>" context. Asserts that the
    /// format string used at pipeline.rs error-emission preserves
    /// both layers.
    #[test]
    fn check_format_preserves_anyhow_chain() {
        let leaf: Error = anyhow!("expected value at line 1 column 1");
        let chained = Err::<(), _>(leaf)
            .context("parsing JSON in /tmp/x.ail.json")
            .unwrap_err();
        let formatted = format!("check: {chained:#}");
        assert!(
            formatted.contains("parsing JSON in /tmp/x.ail.json"),
            "top-level context missing; got: {formatted}",
        );
        assert!(
            formatted.contains("expected value at line 1 column 1"),
            "leaf cause missing; got: {formatted}",
        );
    }
}
```

- [ ] **Step 2: Run the test — verify it does NOT compile or fails informatively**

Run: `cargo test --manifest-path experiments/2026-05-12-cross-model-authoring/harness/Cargo.toml check_format_preserves_anyhow_chain`

Expected: the test PASSES because we wrote `{chained:#}` directly
in the test body, NOT because we're calling the production
formatter. This is acceptable — the test pins the *property* that
`{:#}` preserves the chain. The actual RED-GREEN dance happens in
Task 2 below, where the production line at `pipeline.rs:118` is
changed.

> Reviewer note: a more direct RED-first test would call a
> Boss-extractable formatter helper from production code and assert
> against it. The current production code inlines the format
> string at the call site (`format!("check: {e}")` is local to a
> match arm), and extracting it to a helper just for testability
> would be over-engineering for a two-character fix. The pinning
> test in this task plus the manual code-path inspection in Task 2
> together close the loop.

## Task 2: GREEN — switch pipeline.rs:118 to alternate Display

**Files:**
- Modify: `experiments/2026-05-12-cross-model-authoring/harness/src/pipeline.rs:118`

- [ ] **Step 1: Read the current line**

Run: `sed -n '115,122p' experiments/2026-05-12-cross-model-authoring/harness/src/pipeline.rs`

Expected output (verbatim):

```
        Err(e) => {
            return Ok(PipelineCapture {
                error: Some(format!("check: {e}")),
                stdout: String::new(),
                stderr: e.to_string(),
            });
        }
```

- [ ] **Step 2: Apply the change**

In `pipeline.rs:118`, change:

```rust
                error: Some(format!("check: {e}")),
```

to:

```rust
                error: Some(format!("check: {e:#}")),
```

(Two-character delta: `{e}` → `{e:#}`. No other lines change.)

- [ ] **Step 3: Re-read to confirm**

Run: `sed -n '115,122p' experiments/2026-05-12-cross-model-authoring/harness/src/pipeline.rs`

Expected output (verbatim):

```
        Err(e) => {
            return Ok(PipelineCapture {
                error: Some(format!("check: {e:#}")),
                stdout: String::new(),
                stderr: e.to_string(),
            });
        }
```

- [ ] **Step 4: Run the unit test from Task 1**

Run: `cargo test --manifest-path experiments/2026-05-12-cross-model-authoring/harness/Cargo.toml check_format_preserves_anyhow_chain`

Expected: PASS.

## Task 3: Full harness test sweep — no regressions

**Files:** (none modified; verification only)

- [ ] **Step 1: Run the full harness test suite**

Run: `cargo test --manifest-path experiments/2026-05-12-cross-model-authoring/harness/Cargo.toml`

Expected: **14 passed** (the previous 13 + the new `check_format_preserves_anyhow_chain`).
Suite breakdown:
- inline `--lib` unit tests: 6 (5 strip_locations + 1 new pipeline)
- integration `strip_locations`: 5
- integration `verify_references`: 1
- integration `mock_full_run`: 1
- integration `budget_abort`: 1

- [ ] **Step 2: cargo check the crate**

Run: `cargo check --manifest-path experiments/2026-05-12-cross-model-authoring/harness/Cargo.toml`

Expected: clean (no new warnings introduced by the edit).

---

## Per-iter journal entry

After all tasks complete, write
`docs/journals/2026-05-12-iter-ms.1.md` (≤200 words) covering:

- What the bug was and how it was discovered (during ms.2 planning recon)
- Why `{:#}` is the right fix (alternate Display joins chain with `: `, survives strip_locations)
- Why this was a separate iter from ms.2 (precedes the live IONOS spend; cheap fix should land before any further runs)
- Test count after: 14 (up from 13)

Add a one-line entry to `docs/journals/INDEX.md` pointing at the
new file.
