build(runner): reduce development debug information (#18307)

## Thinking Path

> - Paperclip is the open source app people use to manage AI agents for
work.
> - Agents and contributors compile the Rust runner inside workspaces
with limited storage.
> - Default development builds include full debug information in many
test executables.
> - A controlled Linux build used 11.54 GiB with those defaults.
> - This pull request uses line-only debug information for the
development profile and its test profile.
> - The measured build used 4.35 GiB and retained source-line
information for backtraces.

## Linked Issues or Issue Description

**What existing behavior does this improve?**

The storage used by Rust development builds and default-profile test
builds in `packages/paperclip-runner`.

**Current behavior**

The workspace uses Cargo's full development debug information. A clean
Linux ARM64 comparison on source
`d2280108f56872a6052a5011649a73cef9aac206`, Rust 1.97.1, and four build
jobs used 11.54 GiB for the test build output. This can exceed a small
sandbox's entire disk allocation.

**Proposed behavior**

Set `[profile.dev] debug = "line-tables-only"` in the Rust workspace
manifest. The default test profile inherits it. The same comparison used
4.35 GiB, a 62.3% reduction. Incremental compilation stays enabled.
Release settings stay as they are.

**Reason and benefit**

Reduce build storage while preserving file names and line numbers in
backtraces. This avoids removing all debug information or changing which
tests compile.

**Breaking changes**

Default development builds omit type and local-variable debugger
information. Contributors can restore it with
`CARGO_PROFILE_DEV_DEBUG=2` and `CARGO_PROFILE_TEST_DEBUG=2`. There are
no product API changes.

Related: #18172 handles workspace export after disk exhaustion. #16500
proposes separate CI-only debug settings and test scheduling changes.
This PR sets the workspace default and remains compatible with explicit
environment overrides. Searches found no existing PR for
`line-tables-only`.

## What Changed

- Set the runner workspace development debug level to
`line-tables-only`.
- Document test-profile inheritance and the full-debug environment
overrides.

## Verification

- Prior controlled comparison: fresh target directory per setting,
shared dependency downloads outside timing, identical source and
lockfile, Rust/Cargo 1.97.1, Linux ARM64, four build jobs, and a six-GiB
memory limit. First compile library tests, then all test targets with
`cargo test --locked --offline -p paperclip-runner-core --no-run
durable::`. Both configurations compiled all 32 test executables.
Measure the target directory with `du -sk`, counting hard links once.
Full debug: 11.54 GiB. Line-only debug: 4.35 GiB. These numbers exclude
source, registry, image, and Node dependencies. The initial benchmark
setup omitted an external fixture; that run was discarded after adding
the fixture from the same source revision.
- Current manifest verification passed on Linux ARM64 / Rust 1.97.1 with
profile environment overrides unset: all 32 test executables compile,
all 98 durable unit tests pass, and development binaries build. Verbose
compiler commands show `-C debuginfo=line-tables-only` and an
incremental directory for both the library and its test harness. This
verifies test-profile inheritance from the manifest. The fresh target
directory is 4.36 GiB on the updated source. No new test asserts the
manifest text; validation uses the actual compiler and existing tests.
- `cargo metadata --manifest-path
packages/paperclip-runner/runner/Cargo.toml --locked --offline --no-deps
--format-version 1` and `git diff --check` pass.
- [CI passed on commit
`14d798139f5ff04414c6acbe15cec04e9b680a00`](https://github.com/paperclipai/paperclip/actions/runs/41059532543),
including the `ci / verify` aggregate. The separate native Docker Runner
check also passed. The final check inventory has 55 successful checks,
four expected skips, and the neutral review described below; the legacy
security status passed. Two first-attempt worker interruptions required
one targeted retry each: Runner Vitest 2/2 received a shutdown signal
during native integration verification, and chat 1/3 lost communication
with GitHub. The exact interruption causes remain unknown. The Runner
retry passed 132 files / 2,321 tests (two existing skips), then four
native integration files / 127 tests (five existing skips). The chat
retry and final aggregate passed. The successful retries establish
recovery on this commit; they do not establish the cause of either
original interruption.
- Greptile reviewed the current commit at 5/5 with no findings. The
separate Paperclip review execution did not complete and returned a
neutral check without an assessment. This is not counted as a completed
review.

## Risks

- Native debugger inspection of types and local variables needs a
full-debug override. Source-line backtraces remain available.
- Changing debug settings rebuilds affected artifacts. Existing
full-debug outputs may remain until the contributor cleans their target
directory.
- The measured savings are from Linux ARM64 and the cited source
revision. Other platforms and workloads can differ. This is a
build-profile change, not a sandbox capacity increase.

## Model Used

OpenAI GPT-6 through Codex, with reasoning, repository tools, shell
execution, and Linux build measurements. The session does not expose a
more specific serving model ID or context-window size.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/paperclip-runner/README.md

@@ -552,6 +552,13 @@ pnpm --filter @paperclipai/paperclip-runner verify
 The verification command requires a stable Rust toolchain with `cargo` on
 `PATH`, in addition to Node.js 24.11+ and pnpm 9+.
 
+Rust development builds use `debug = "line-tables-only"` to reduce build storage
+while retaining file names and line numbers in backtraces. The default test
+profile inherits this setting. Incremental compilation remains enabled, and
+release profiles keep their existing settings. For full debugger support,
+including local variables and types, set `CARGO_PROFILE_DEV_DEBUG=2` and
+`CARGO_PROFILE_TEST_DEBUG=2` for the build or test command.
+
 Minimal Debian/Ubuntu hosts without root access can extract the required
 Playwright browser libraries into a user-owned cache and run the same acceptance
 sequence with:

packages/paperclip-runner/runner/Cargo.toml

@@ -2,6 +2,9 @@
 members = ["crates/runner-core"]
 resolver = "2"
 
+[profile.dev]
+debug = "line-tables-only"
+
 [workspace.package]
 version = "0.0.0"
 edition = "2021"