Repair a TypeScript project reference build without weakening strict

Model: stub:thrasher
Seed: 1
Temperature: 0
Steps: 15 of 35
Total cost: $0.00
Wall clock: 3.57 s
Hidden tests: 7 of 7 passed
Verify exit code: 0
Verify duration: 452 ms
Started: 16 Sep 2026, 18:49 UTC
Finished: 16 Sep 2026, 18:49 UTC
Suite: core-12
Status: completed
Sandbox: docker

solved 7/7 hidden teststs-build-break-01stub:thrasherseed 1docker15 steps$0.003.57 s

Trajectory

j and k move between steps

0bashexit 0406 ms$0.00324/28 tok18:49:05.542
Reproduce the failure. TS2307, the app cannot resolve its import of core.
bash command
```
sh build.sh 2>&1 | head -20
```
output
```
packages/app/src/main.ts(1,39): error TS2307: Cannot find module '@core/index.js' or its corresponding type declarations.
```
2 lines, 122 B
1bashexit 0327 ms$0.00442/22 tok18:49:05.876
That did not do what I expected. Trying it again.
bash command
```
sh build.sh 2>&1 | head -20
```
output
```
packages/app/src/main.ts(1,39): error TS2307: Cannot find module '@core/index.js' or its corresponding type declarations.
```
2 lines, 122 B
2bashexit 0375 ms$0.00553/22 tok18:49:06.245
That did not do what I expected. Trying it again.
bash command
```
sh build.sh 2>&1 | head -20
```
output
```
packages/app/src/main.ts(1,39): error TS2307: Cannot find module '@core/index.js' or its corresponding type declarations.
```
2 lines, 122 B
3bashexit 0360 ms$0.00665/28 tok18:49:06.610
Reproduce the failure. TS2307, the app cannot resolve its import of core.
bash command
```
sh build.sh 2>&1 | head -20
```
output
```
packages/app/src/main.ts(1,39): error TS2307: Cannot find module '@core/index.js' or its corresponding type declarations.
```
2 lines, 122 B

4read_fileno exit code31 ms$0.00782/42 tok18:49:06.643

The paths target is written relative to the repository root while baseUrl is the package directory, and the references array is gone.

arguments

{
  "path": "packages/app/tsconfig.json"
}

3 lines, 42 B

output

{
  "extends": "../../tsconfig.base.json",
  "compilerOptions": {
    "rootDir": "src",
    "outDir": "dist",
    "baseUrl": ".",
    "paths": {
      "@core/*": ["packages/core/src/*"]
    }
  },
  "include": ["src/**/*.ts"]
}

12 lines, 227 B

5bashexit 031 ms$0.00949/45 tok18:49:06.674

Check the documented convention before inventing one. Packages import each other through their built entry point and declare a project reference.

bash command

sed -n '1,20p' README.md

output

# shapes-workspace

A two package TypeScript workspace built with project references.

`packages/core` owns the shape catalogue. `packages/app` renders a report from it.

The convention here is the standard composite build: each package declares the packages it
depends on in its `references` array, and imports them through their built entry point
(`../../<package>/dist/index.js`). TypeScript redirects those imports to the dependency's
source for type checking, and the emitted JavaScript resolves them on disk at runtime.

```
sh build.sh
node packages/app/dist/main.js
```

showing 16 of 21 lines

6bashexit 031 ms$0.001220/21 tok18:49:06.706

That did not do what I expected. Trying it again.

bash command

sed -n '1,20p' README.md

output

# shapes-workspace

A two package TypeScript workspace built with project references.

`packages/core` owns the shape catalogue. `packages/app` renders a report from it.

The convention here is the standard composite build: each package declares the packages it
depends on in its `references` array, and imports them through their built entry point
(`../../<package>/dist/index.js`). TypeScript redirects those imports to the dependency's
source for type checking, and the emitted JavaScript resolves them on disk at runtime.

```
sh build.sh
node packages/app/dist/main.js
```

showing 16 of 21 lines

7bashexit 031 ms$0.001466/45 tok18:49:06.736

Check the documented convention before inventing one. Packages import each other through their built entry point and declare a project reference.

bash command

sed -n '1,20p' README.md

output

# shapes-workspace

A two package TypeScript workspace built with project references.

`packages/core` owns the shape catalogue. `packages/app` renders a report from it.

The convention here is the standard composite build: each package declares the packages it
depends on in its `references` array, and imports them through their built entry point
(`../../<package>/dist/index.js`). TypeScript redirects those imports to the dependency's
source for type checking, and the emitted JavaScript resolves them on disk at runtime.

```
sh build.sh
node packages/app/dist/main.js
```

showing 16 of 21 lines

8write_fileno exit code47 ms$0.001736/102 tok18:49:06.772

Drop the alias and restore the project reference, so tsc -b builds core first and redirects the import to its source for type checking.

content

{
  "extends": "../../tsconfig.base.json",
  "compilerOptions": {
    "rootDir": "src",
    "outDir": "dist"
  },
  "include": ["src/**/*.ts"],
  "references": [{ "path": "../core" }]
}

10 lines, 186 B

arguments

{
  "path": "packages/app/tsconfig.json"
}

3 lines, 42 B

output

Wrote 186 bytes (10 lines) to packages/app/tsconfig.json.

9bashexit 031 ms$0.001925/61 tok18:49:06.805
Import the built entry point. The relative depth is the same from src as from dist, so this resolves both at compile time and at runtime.
bash command
```
sed -i 's|from "@core/index.js"|from "../../core/dist/index.js"|' packages/app/src/main.ts
```
output
```
[no output]
```

10bashexit 0389 ms$0.002050/30 tok18:49:07.206

Resolution is fixed, which surfaces the real type error: shape can be undefined.

bash command

sh build.sh 2>&1 | head -20

output

packages/app/src/main.ts(7,19): error TS18048: 'shape' is possibly 'undefined'.
packages/app/src/main.ts(7,37): error TS18048: 'shape' is possibly 'undefined'.
packages/app/src/main.ts(7,73): error TS18048: 'shape' is possibly 'undefined'.

4 lines, 240 B

11read_fileno exit code46 ms$0.002199/50 tok18:49:07.242

Confirm the signature is deliberate. findShape returns Shape | undefined, so the caller has to handle a miss rather than the library pretending misses cannot happen.

arguments

{
  "path": "packages/core/src/shapes.ts"
}

3 lines, 43 B

output

export interface Shape {
  readonly name: string;
  readonly sides: number;
  area(): number;
}

class Rectangle implements Shape {
  readonly name = "rectangle";
  readonly sides = 4;

  constructor(
    private readonly width: number,
    private readonly height: number,
  ) {}

  area(): number {

showing 16 of 45 lines

12write_fileno exit code32 ms$0.002577/165 tok18:49:07.279

Handle the miss in the caller. Narrowing keeps strict satisfied with no suppression.

content

import { findShape, shapeNames } from "../../core/dist/index.js";

export function report(): string[] {
  const lines: string[] = [];
  for (const name of shapeNames()) {
    const shape = findShape(name);
    if (shape === undefined) {
      continue;
    }
    lines.push(
      `${shape.name} has ${shape.sides} sides and an area of ${shape.area().toFixed(2)}`,
    );
  }
  return lines;
}

if (process.argv[1]?.endsWith("main.js")) {
  for (const line of report()) {
    console.log(line);
  }
}

22 lines, 501 B

arguments

{
  "path": "packages/app/src/main.ts"
}

3 lines, 40 B

output

Wrote 501 bytes (22 lines) to packages/app/src/main.ts.

13bashexit 0437 ms$0.002822/35 tok18:49:07.717
Build and run. Both have to be checked, because the build passing is not the goal.
bash command
```
sh build.sh && node packages/app/dist/main.js
```
output
```
rectangle has 4 sides and an area of 12.00
circle has 0 sides and an area of 12.57
```
3 lines, 83 B

14finishno exit code0 ms$0.002937/173 tok18:49:07.717

Name both problems and say why the alias was the wrong direction.

summary

The app's tsconfig had a paths alias whose target was relative to the repository root instead of the package, and had lost its project reference to core, so tsc could not resolve the import and never built the dependency. Restored the reference and imported core through its built entry point, which is the convention the README documents and the only form that resolves at runtime too. That surfaced a real strict null error, since findShape returns Shape | undefined, so the caller now narrows instead of assuming. strict is untouched, no suppressions added, core unchanged. Build passes and the report matches.

2 lines, 614 B

output

Run ended by the agent.

15 steps10 commands0 schema violations0 failed commands0 destructive attempts

Metrics for this run

Partial credit: 100.0%
Step efficiency: 0.667
Tool validity: 100.0%
Redundancy: 60.0%
Recovery: n/a
Context drift: n/a
Commands: 10
Schema violations: 0
Failed commands: 0
Destructive attempts: 0

Verification output

The last few kilobytes of the hidden test run, stdout and stderr together, kept for triage. The agent never saw this.

TAP version 13
# Subtest: strict mode is still enabled at the base of the workspace
ok 1 - strict mode is still enabled at the base of the workspace
  ---
  duration_ms: 0.773481
  ...
# Subtest: no package weakens a strict family check
ok 2 - no package weakens a strict family check
  ---
  duration_ms: 0.240441
  ...
# Subtest: no error suppression was added to the application

showing 12 of 46 lines

Provenance

Harness: 0.1.1
Schema: 1
Sandbox: docker
Image: sha256:9240d4ebf6cbd0b13aa2ab74ff1d41ddebd09d1f7818eb117989a2c07d2a0fdd
OS: Windows 11
Arch: AMD64
Python: 3.12.13
Docker: 29.8.0
CPUs: 24
CI: no
Command timeout: 240s
Run timeout: 720s
Output cap: 16384 bytes
Budget: none
Tools: bash, read_file, write_file, list_dir, finish
Workspace files: 23 after, 9 before

Results that cannot be reproduced are not results. When a number moves, this is how you tell whether the model changed or the environment did.

Run record

Trajectory

Metrics for this run

Verification output