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Merge pull request #58 from link-foundation/issue-57-3b7cfd0944e2
fix: handle du exit code for missing paths in sandbox script (Issue #57)
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‎.changeset/fix-du-exit-code-regression.md‎

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Fix CI failure caused by `du` exit code regression introduced in Issue #55 fix: only pass paths that exist to `du -sb` to avoid killing the script under `set -euo pipefail` when Homebrew or Rust installation dirs are absent.

‎docs/case-studies/issue-57/CASE-STUDY.md‎

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# Case Study: CI/CD Failed — `du` Exit Code Regression from Issue #55 Fix (Issue #57)
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## Summary
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The CI/CD "Measure Disk Space and Update README" workflow failed with **exit code 1** on the merge of PR #56 (the Issue #55 fix). The script `scripts/measure-disk-space.sh` exited early inside the sandbox user sub-script when measuring Homebrew. The fix for Issue #55 introduced a regression: `du -sb` is called on paths that may not exist, and with `set -euo pipefail` active, a non-zero `du` exit code kills the script before it can record 0 MB and continue.
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## Issue Reference
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- **Issue**: [#57 — We have CI/CD failed](https://github.com/link-foundation/sandbox/issues/57)
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- **Failed CI run**: https://github.com/link-foundation/sandbox/actions/runs/22347524656/job/64665886012
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- **Log file**: `docs/case-studies/issue-57/ci-job-64665886012.log`
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- **Triggered by**: Merge of PR #56 (commit `f274bfab` — "1.3.10: Fix language runtime size measurements")
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## Timeline of Events
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| Time (UTC) | Event |
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|---|---|
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| 2026-02-22T01:47:26Z | **Last successful run** (PR #52, commit `03a9d8da`) — Homebrew failed silently, recorded 0 MB |
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| 2026-02-24T10:48:21Z | PR #56 merged (`f274bfab`) — introduces the Issue #55 fix (du-based measurement for Homebrew/Rust) |
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| 2026-02-24T10:48:24Z | CI job starts |
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| 2026-02-24T10:58:42Z | Opam + Rocq/Coq recorded (1307.03 MB) |
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| 2026-02-24T10:58:42Z | Homebrew installer runs — exits with "Insufficient permissions" |
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| 2026-02-24T10:58:44Z | **Script exits with code 1** — all subsequent steps skipped |
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## Failure Evidence
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From `ci-job-64665886012.log` (lines 2207–2218):
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```
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==> Running in non-interactive mode because `$NONINTERACTIVE` is set.
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/usr/bin/ldd: line 41: printf: write error: Broken pipe
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/usr/bin/ldd: line 43: printf: write error: Broken pipe
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==> Checking for `sudo` access (which may request your password)...
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Insufficient permissions to install Homebrew to "/home/linuxbrew/.linuxbrew" (the default prefix).
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Alternative (unsupported) installation methods are available at:
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https://docs.brew.sh/Installation#alternative-installs
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Please note this will require most formula to build from source, a buggy, slow and energy-inefficient experience.
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We will close any issues without response for these unsupported configurations.
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##[error]Process completed with exit code 1.
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```
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---
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## Root Cause Analysis
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### Root Cause 1: `du` returns exit code 1 for non-existent paths; `set -euo pipefail` kills the script
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**Location:** `scripts/measure-disk-space.sh` (sandbox sub-script, Homebrew section, around line 588)
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**The buggy code** (introduced by the Issue #55 fix in commit `3471bf8`):
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```bash
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if install_homebrew; then
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cleanup_for_measurement
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brew_bytes=$(du -sb /home/linuxbrew/.linuxbrew "$HOME/.linuxbrew" 2>/dev/null | awk '{sum+=$1} END{print sum+0}')
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...
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```
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**What happens step by step:**
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1. `install_homebrew()` is called. Inside it:
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```bash
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NONINTERACTIVE=1 /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)" || true
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```
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The Homebrew installer checks `sudo` access and write permissions. The `sandbox` user has no NOPASSWD sudo, so `sudo -n -l mkdir` fails. Even though `/home/linuxbrew/.linuxbrew` is owned by sandbox (created by the outer script), the Homebrew installer exits with code 1. The `|| true` suppresses this, so `install_homebrew()` returns **0** (success).
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2. Because `install_homebrew` returns 0, the `if install_homebrew; then` branch is taken.
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3. Inside the branch, `du -sb /home/linuxbrew/.linuxbrew "$HOME/.linuxbrew"` is run:
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- `/home/linuxbrew/.linuxbrew` exists (created by the outer script, but empty — brew install failed)
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- `"$HOME/.linuxbrew"` does NOT exist (sandbox user HOME = `/home/sandbox`, no `.linuxbrew` there)
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- `du` exits with **code 1** because one argument doesn't exist
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- The `2>/dev/null` suppresses the stderr error message, but NOT the exit code
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- With `set -euo pipefail` active in the sandbox sub-script, the non-zero exit from `du` kills the entire script
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4. The sandbox sub-script exits with code 1, which propagates to the outer `sudo -i -u sandbox bash /tmp/sandbox-measure.sh` call, which propagates to the CI step.
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**Reproducer:**
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```bash
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bash -c 'set -euo pipefail; result=$(du -sb /tmp/nonexistent_dir 2>/dev/null | awk "{sum+=\$1} END{print sum+0}"); echo "$result"'
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# → exits with code 1 (not 0)
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```
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### Root Cause 2: Homebrew installer permission check vs. sandbox user
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The Homebrew installer (as of Jan 2026) aborts when ALL these conditions are true:
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- `HOMEBREW_PREFIX` (`/home/linuxbrew/.linuxbrew`) is not writable, OR
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- `/home/linuxbrew` is not writable, OR
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- `/home` is not writable, AND
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- `have_sudo_access()` returns false
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With `NONINTERACTIVE=1`, `have_sudo_access()` runs `sudo -n -l mkdir`. The sandbox user was added to the `sudo` group via `usermod -aG sudo sandbox`, but GitHub Actions runners only grant passwordless sudo to the `runner` user. The sandbox user has no NOPASSWD entry, so `sudo -n` fails.
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The outer script creates `/home/linuxbrew/.linuxbrew` and `chown -R sandbox:sandbox /home/linuxbrew` (as root), which should make the directory writable by sandbox. However, this issue represents a brittle dependency: the permission pre-setup in the outer script must work correctly for every run. If something changes (runner image update, timing issue), Homebrew will fail.
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**Note**: In the previous run (commit `03a9d8da`), Homebrew also failed with the same "Insufficient permissions" error, but `measure_install "Homebrew" "Package Manager" install_homebrew` correctly handled the failure by recording 0 MB and continuing.
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---
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## Sequence of Events (Root Cause 1 in detail)
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```
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outer script (root) runs
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→ creates /home/linuxbrew/.linuxbrew, chowns to sandbox
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→ writes /tmp/sandbox-measure.sh
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→ runs: sudo -i -u sandbox bash /tmp/sandbox-measure.sh /tmp/disk-space-*.json
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sandbox-measure.sh (runs as sandbox user, set -euo pipefail)
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→ measures Bun, deno, nvm, pyenv, Go, Rust, SDKMAN, Kotlin, Lean, Opam
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→ cleanup_for_measurement
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→ install_homebrew() called:
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NONINTERACTIVE=1 /bin/bash -c "$(brew install.sh)" || true
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→ brew installer: "Insufficient permissions" → exits 1
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→ || true → install_homebrew returns 0
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→ [if branch taken because install_homebrew returned 0]
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→ brew_bytes=$(du -sb /home/linuxbrew/.linuxbrew "$HOME/.linuxbrew" 2>/dev/null | awk ...)
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→ /home/linuxbrew/.linuxbrew exists (empty)
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→ $HOME/.linuxbrew does NOT exist
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→ du exits with code 1
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→ 2>/dev/null silences the error message
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→ EXIT CODE 1 propagates through command substitution $()
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→ set -euo pipefail kills the script HERE
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← sandbox-measure.sh exits with code 1
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outer script exits with code 1
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CI step fails
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All subsequent steps (Update README, Validate, Commit, Push) are SKIPPED
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```
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---
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## Comparison: Before vs. After Issue #55 Fix
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### Before (commit `03a9d8da`, successful run 2026-02-22):
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```bash
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measure_install "Homebrew" "Package Manager" install_homebrew
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```
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The `measure_install` wrapper calls `install_homebrew` inside an `if "$@"; then / else` block:
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```bash
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if "$@"; then
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...
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else
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log_warning "Installation of $name failed"
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add_measurement "$name" "$category" 0 0
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fi
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```
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Since `install_homebrew` returns 0 (due to `|| true`), the success branch runs, calculates `df`-based size (which was inaccurate but at least didn't crash), and continues.
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### After (commit `3471bf8`, failing run 2026-02-24):
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```bash
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if install_homebrew; then
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brew_bytes=$(du -sb /home/linuxbrew/.linuxbrew "$HOME/.linuxbrew" 2>/dev/null | awk ...)
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...
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```
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`install_homebrew` returns 0 (same as before), but now `du` is called on paths that may not exist, and its exit code is not handled. Result: script dies.
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---
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## Fix
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The fix ensures `du` does not cause script failure when directories don't exist. There are two approaches:
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### Option A: Only pass paths that exist to `du`
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```bash
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cleanup_for_measurement
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if install_homebrew; then
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cleanup_for_measurement
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brew_paths=()
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[[ -d /home/linuxbrew/.linuxbrew ]] && brew_paths+=(/home/linuxbrew/.linuxbrew)
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[[ -d "$HOME/.linuxbrew" ]] && brew_paths+=("$HOME/.linuxbrew")
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if [[ ${#brew_paths[@]} -gt 0 ]]; then
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brew_bytes=$(du -sb "${brew_paths[@]}" 2>/dev/null | awk '{sum+=$1} END{print sum+0}')
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else
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brew_bytes=0
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fi
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brew_mb=$(awk "BEGIN {printf \"%.2f\", $brew_bytes / 1000000}")
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add_measurement "Homebrew" "Package Manager" "$brew_bytes" "$brew_mb"
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else
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log_warning "Installation of Homebrew failed"
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add_measurement "Homebrew" "Package Manager" 0 0
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fi
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```
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### Option B: Use `|| true` to suppress `du` exit code (simpler)
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```bash
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brew_bytes=$(du -sb /home/linuxbrew/.linuxbrew "$HOME/.linuxbrew" 2>/dev/null | awk '{sum+=$1} END{print sum+0}') || brew_bytes=0
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```
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**Option A** is more correct because it avoids measuring partial data silently; **Option B** is a minimal change. The same fix applies to the Rust measurement, though Rust paths (`$HOME/.rustup` and `$HOME/.cargo`) are typically both present after a successful install.
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The same pattern in the outer script (lines 509–517 for Rust) should also be reviewed, though it doesn't currently fail because Rust installation succeeds and both directories exist.
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---
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## Related Issues
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- **Issue #55**: Incorrect language runtime size measurements (introduced the regression)
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- **Issue #46**: Relative path resolution for sandbox user JSON file
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- **Issue #49**: sed-based JSON manipulation failures
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## External Resources
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- [Homebrew install.sh permission check](https://github.com/Homebrew/install/blob/main/install.sh) — the `elif ! [[ -w "${HOMEBREW_PREFIX}" ]] && ... && ! have_sudo_access` condition
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- [Homebrew Discussion #5929](https://github.com/orgs/Homebrew/discussions/5929) — "Insufficient permissions to install Homebrew to /home/linuxbrew/.linuxbrew"
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- [Homebrew Discussion #4212](https://github.com/orgs/Homebrew/discussions/4212) — sudo-less installation discussion
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- [Homebrew Issue #714](https://github.com/Homebrew/install/issues/714) — NONINTERACTIVE mode suppresses sudo password prompt

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