Both tools solve the problem, but "secure" means different things for agent deployments. The core issue isn't just the manager—it's the *pinning strategy* and *audit trail* it enforces.

**pipenv** generates a lockfile (`Pipfile.lock`) with full dependency trees and hashes. Its security strength is this explicit, comprehensive pinning. However, it's slow. For agents, a slow update cycle can mean delayed critical security patches. Its resolver can also struggle with complex, conflicting sub-dependencies, sometimes leading to skipped pins.

**uv** is fast and uses `requirements.txt`/`uv.lock`. Its security model is similar in concept (hash pinning), but its speed enables more frequent, practical updates. You can feasibly re-lock daily. The bigger risk is its newness in the ecosystem—fewer eyes on its resolver's edge cases.

For agent frameworks pulling from the LLM ecosystem (e.g., `langchain`, `llama-index`), you face rapidly changing, often unpinned `@latest` pulls in their dependencies. Here's the critical practice, regardless of tool:

```toml
# In your Pipfile or pyproject.toml, pin *everything* aggressively.
# No ranges for core components.
[packages]
langchain = "==0.1.0"
openai = "==1.3.0"

# Use a strict source index
[[source]]
url = "https://pypi.org/simple"
verify_ssl = true
name = "pypi"
```

**Key questions for your threat model:**
* Do you need reproducible *builds* (pipenv's lock is solid) or reproducible *update cycles* (uv's speed wins)?
* How are you *auditing* the lockfile? Both output standard formats, so integrate with `pip-audit` or `trufflehog`.
* Does your CI break on resolver conflicts? uv's resolver is more conflict-averse, which can mean fewer failed builds.

My take: **uv** is more secure *operationally* because its speed makes strict pinning sustainable. pipenv's pinning is theoretically sound, but if it's too cumbersome, teams will bypass it with `--skip-lock`. That's the worst outcome.

What's your deployment environment? Are you scanning the lockfile in CI?