A missing documentation database is not rebuilt automatically

Nobody has claimed this yet.

This issue was triaged from [`bugs/dan/1-building-doc-databases`](https://github.com/Macaulay2/M2/blob/388c1ff0ce30d83751dea7bc7eac77fdc1305dd7/bugs/dan/1-building-doc-databases), one of the 857 files removed from the pre-GitHub `bugs/` tree by [`d2c8d27826`](https://github.com/Macaulay2/M2/commit/d2c8d27826) and catalogued in [#36](https://github.com/Macaulay2/M2/issues/36). **The commentary below was written by Claude (Claude Opus 5, via Claude Code)**, not by @d-torrance, whose account posted it -- please weigh it accordingly.

### The original file, verbatim

```text
The doc databases for packages may not be getting built if we start fresh with
just the CommonStagingArea files, because *.installed is there. (FIXED)

It would be nice also if a missing database could be rebuilt automatically, provided
the directory is writable.
```

### Where it stands today

The file settles its own first half — it says `(FIXED)` for the `.installed` problem. The second half is
unmet.

### What is missing

`installPackage` touches `.installed` when a run completes (`installPackage.m2:846-849`), but nothing
detects a **missing documentation database** and rebuilds it, writable directory or not. So a prefix
whose `.installed` stamp survives while its `rawdocumentation` database does not is a state M2 cannot
recover from on its own, even though everything needed to rebuild is present.

### Why that state arises

Exactly as the file describes: starting from a partial tree — the staging area, a copied prefix, an
interrupted install — leaves the stamp and loses the database. `tallyInstalledPackages` then skips the
package entirely ("maybe installation was interrupted, so ignore this package"), so the documentation is
silently absent rather than rebuilt.

### Nearby but not the same

**#1643** wants one documentation database per prefix instead of per package, for speed; **#776** wants
the open database files bounded by an LRU cache. Neither rebuilds a missing one.

_{`open` · disposition `issue` · source of truth: [`bug-triage/catalog.tsv`](https://github.com/d-torrance/M2/blob/bug-triage/bug-triage/catalog.tsv)}

Start in installPackage.m2 around lines 846-849, then trace tallyInstalledPackages and the handling of the rawdocumentation database. Reproduce the state where .installed remains but the documentation database is missing, and verify that a writable installation can recover it automatically without skipping the package.

Written by the indexing model from the issue text.