docs: fan-out support level overstated, missing known limitations

[justapithecus]

Context

Auditing v0.6.0 fan-out for a real workload (discovery → gallery scraping with storage.put() sidecars) surfaced three functional gaps that aren't documented anywhere.

Findings

1. SUPPORT.md: Fan-out listed as "Supported"

Fan-out (--depth) | Supported is too strong given the blockers below. Should be Experimental at minimum until the gaps are closed.

2. PUBLIC_API.md: Known Limitations missing three functional gaps

None of these appear in the Known Limitations section:

• storage.put() is nil for child runs — FileWriter is intentionally nil (noted in code comments as a deferred refactor), meaning any script that writes sidecar files will silently fail or panic as a child run
• target resolution is unfrozen — currently treated as a literal file path, but the implementation plan flags this as an open question. Users committing to a path format risk rework
• category inheritance — child runs inherit the root's source and category, so a discovery root (category=discover) produces gallery children that land under discover instead of gallery in Lode partitions. No per-enqueue override exists

3. Fan-out-chain example doesn't warn about the boundary

The example uses emit.item() only (no storage.put()), which is fine — but there's no doc note warning users that storage.put() isn't wired for children. A user extrapolating from the example to a real workload with sidecar files would hit a silent failure.

4. CONTRACT_CLI.md fan-out section stated as fact without caveats

The --depth, --max-runs, --parallel flags are documented as stable contract, but the underlying implementation has known incomplete plumbing. At minimum, the contract should note:

• storage.put() not available in child runs
• category inherited from root (no per-child override)
• target resolution semantics may change

Suggested fixes

• SUPPORT.md: Fan-out (--depth) | Experimental
• PUBLIC_API.md Known Limitations: add the three gaps above
• Fan-out-chain example or its README: note that storage.put() is not available in child runs
• CONTRACT_CLI.md: add a caveats subsection under fan-out

References

• PR feat(runtime): ✨ add fan-out operator for derived work execution #117 (fan-out operator implementation)
• Design docs docs(design): 📝 add ingress models exploration document #115, docs(design): 📝 replace crawl mode with derived work execution via fan-out flags #116
• Implementation plan: FileWriter deferred, target resolution flagged as open question