fix: .bashrc merge algorithm corrupted multi-line shell constructs (issue #66)

[konard]

Fixes #66

Root Cause

When running bash inside an already-running bash session in the sandbox container, bash sources ~/.bashrc and hits a fatal syntax error:

bash: /home/sandbox/.bashrc: line 167: syntax error: unexpected end of file

The error occurs only on explicit bash invocations (not at container start) because .bashrc has an early-return guard:

case $- in *i*) ;; *) return;; esac

entrypoint.sh is non-interactive → returns early, never reaches the broken block. An explicit bash is interactive → executes the full .bashrc → hits the unclosed if.

Root cause: The .bashrc merge algorithm in the Dockerfile used line-level deduplication (grep -qxF "$line"). Since Ubuntu's base .bashrc already contains standalone fi lines (closing its built-in if blocks), the closing fi of the Perlbrew if [ -n "$PS1" ]; then ... fi block was silently deduplicated away, leaving an unclosed if.

Verified with experiments/test-bashrc-merge.sh:

Old algorithm: /tmp/.bashrc-merged: line 57: syntax error: unexpected end of file → bug confirmed

Solution

Fix 1: Section-Header Deduplication

Replace line-level deduplication with section-header deduplication in both Dockerfiles. Each language's .bashrc block starts with a unique # <Tool> configuration comment. The new algorithm:

• Checks if the section header is already in the base .bashrc
• If NOT present: appends the header and all subsequent lines (including fi, done, etc.) as a complete unit
• If present: skips the entire section

This preserves all multi-line shell constructs intact and handles cross-language deduplication correctly (e.g., both java/install.sh and kotlin/install.sh write # SDKMAN configuration — the second is correctly skipped as a whole).

Fix 2: POSIX-Compatible SDKMAN Syntax

Replace [[ -s ... ]] && source with [ -s ... ] && . in SDKMAN .bashrc snippets. Ubuntu's /bin/sh is dash — bash-specific [[ ]] and source would fail if .bashrc is ever sourced from a POSIX shell script.

Files Changed

File	Change
Dockerfile	Section-header deduplication in bashrc merge RUN step
ubuntu/24.04/full-sandbox/Dockerfile	Same fix
ubuntu/24.04/java/install.sh	POSIX [ ] and . instead of [[ ]] and source
ubuntu/24.04/kotlin/install.sh	Same fix
ubuntu/24.04/full-sandbox/install.sh	Same fix

Verification

experiments/test-bashrc-merge-fix.sh — 13/13 tests pass:

• Old algorithm produces syntax error (bug reproduced ✓)
• New algorithm produces valid .bashrc (fix confirmed ✓)
• SDKMAN section appears exactly once (kotlin dedup works ✓)
• Perlbrew if/fi block is complete and balanced ✓
• No [[ ]] bash-specific syntax in merged output ✓

Case Study

Full root cause analysis, timeline, and solution in docs/case-studies/issue-66/CASE-STUDY.md.

🤖 Generated with Claude Code

[konard]

🤖 Solution Draft Log

This log file contains the complete execution trace of the AI solution draft process.

💰 Cost estimation:

• Public pricing estimate: $2.894386
• Calculated by Anthropic: $3.444445 USD
• Difference: $0.550059 (+19.00%)
  📎 Log file uploaded as Gist (3464KB)
  🔗 View complete solution draft log

---

Now working session is ended, feel free to review and add any feedback on the solution draft.

[konard]

✅ Ready to merge

This pull request is now ready to be merged:

• All CI checks have passed
• No merge conflicts
• No pending changes

---

Monitored by hive-mind with --auto-restart-until-mergeable flag