gemini: -- separator in build_args breaks all prompts (rc=42)

[nathanschram]

Description

The -- argument separator fix (#194) placed -- before -p in Gemini's build_args(), causing -p to be treated as a positional argument instead of the prompt flag. Every Gemini prompt fails with exit code 42 ("No input provided via stdin").

Impact

All Gemini prompts broken since the -- fix was added in rc11. The runner constructs: gemini ... -- -p <prompt> but POSIX -- means "end of options" so -p is never parsed as a flag.

Reproduction

# Broken (rc11):
gemini --output-format stream-json --approval-mode yolo -- -p "echo hello"
# → "No input provided via stdin" (rc=42)

# Working fix:
gemini --output-format stream-json --approval-mode yolo --prompt="echo hello"
# → Success

Fix

Changed build_args() in runners/gemini.py line 349 from:

args.append("--")
args.extend(["-p", prompt])

to:

args.append(f"--prompt={prompt}")

The --prompt=<value> syntax binds the value directly to the flag, preventing yargs from interpreting a dash-prefixed prompt as a separate flag while keeping -p functional.

Affected files

• src/untether/runners/gemini.py (line 349)
• tests/test_build_args.py (test updated)

Version

v0.35.0rc11

Verified

• Unit tests pass (40/40 in test_build_args.py)
• Integration test: dash-prefixed prompt -help me list files returns correct response
• CLI args in logs show --prompt=... syntax

[nathanschram]

Fixed & verified

Fix applied in 3 files:

• src/untether/runners/gemini.py:349 — args.append(f"--prompt={prompt}")
• tests/test_build_args.py:264 — updated assertion
• tests/test_gemini_runner.py:259 — updated assertion (second test file that referenced -p)

Full verification:

• 1785 unit tests pass, 81.30% coverage
• Ruff format + lint clean
• Telegram integration retest via @untether_dev_bot (chat ut-dev: gemini):
  • ✅ Normal prompt: echo hello world → correct response
  • ✅ Dash-prefixed prompt: -help me list files → file listing (not CLI help)
  • ✅ Model override + prompt: --model gemini-2.5-flash alongside --prompt= → correct
  • ✅ Resume, cancel, multi-tool, long response — all passing
  • ✅ Logs confirm --prompt=... syntax in runner.start args

Ready to include in next rc.