8-059: Unify temp/ and tmp/ into a single tmp/ symlinked to RAM-backed storage

Current behavior

The project's root-level tmp/ is a symbolic link to /tmp/neocities-modernization/
(tmpfs-backed RAM storage). The shell pipeline's ZIP-extraction working space
and the Lua side's worker-script staging both route through this single path.
A helper scripts/ensure-tmp-symlink materialises the symlink on demand and
fails loudly if the path is present but pointing somewhere unexpected.

The first pass of the migration covered scripts/update, the now-deleted
scripts/parallel-word-pages.lua, and .gitignore. A subsequent audit (the
documentation staleness report written to tmp/ during this issue's work)
identified a second pass of consumers that still write to raw /tmp/ or
to the old temp/ path. The current state, after the second pass, is:

• All entry-point scripts that produce ephemeral output call the helper.
• All production source files that previously hardcoded /tmp/... now use

a project-relative path under tmp/. This makes the project portable: a
copy of the repository at a different absolute path produces ephemera at
that new path's tmp/, not at a single shared /tmp/ location that
could collide between parallel copies.

• One library, libs/fuzzy-computing.lua, retains its /tmp/ writes

because the file has zero callers in tracked code and its only exposed
functions are marked DEPRECATED. Migrating its paths would imply a
maintenance commitment the rest of the codebase does not honour. The
file should be deleted in a follow-up.

• The exploratory stub scripts/parallel-word-pages.lua has been removed.

The design it represented has been superseded by issue 10-035 (which
proposes an effil-orchestrator pattern inside src/generate-word-pages.lua
rather than a separate driver script).

Intended behavior

(unchanged) The project has a single ephemeral-output directory, tmp/,
which is a symbolic link to a project-specific subdirectory of the system
tmpfs at /tmp/neocities-modernization/. Every script that writes
ephemeral files goes through this single path.

Every entry point that produces ephemeral output ensures the symlink and
its target exist before any write, via a shared helper. If the symlink
is missing or points to the wrong place, the helper recreates it.

Suggested implementation steps

First pass (completed in commit f45f587c)

1. Created helper scripts/ensure-tmp-symlink. Accepts ${DIR} as first

argument with a hard-coded default, targets /tmp/neocities-modernization/,
idempotent, fails loudly when the path exists but is not the expected
symlink.

1. Updated scripts/update to invoke the helper and to write its

extraction working directory under tmp/extract-... rather than
temp/extract-....

1. Updated .gitignore to ignore tmp instead of temp/.
2. Removed temp/ and tmp/ from the working tree.

Second pass (this commit)

1. Fix scripts/update-words line 30: change BACKUP_DIR="${DIR}/temp/preserved-files-$$"

to BACKUP_DIR="${DIR}/tmp/preserved-files-$$" and call the helper
before the preserve step. This is the bug that motivated re-opening
the issue: the first pass missed this caller, so a subsequent
./run.sh --update-words would have silently re-created temp/ as
a real directory.

1. Migrate scripts/start-ollama-cuda.sh lines 50, 63, 70: replace

/tmp/ollama-cuda.log with a path under the project tmp/. Call the
helper before the first write.

1. Migrate the production Lua source files that previously hardcoded

/tmp/...:

• src/centroid-generator.lua:56 — embedding input shuttle.
• src/similarity-engine.lua:94, 508, 621 — embedding input shuttle

and per-user progress files. The library has a callable DIR since
all entry points pass it; thread it down.

• src/generate-word-pages.lua:155 — word embedding input shuttle.
• src/ollama-manager.lua:49, 151, 158 — ollama log and embedding

test JSON.

1. Migrate the test files:

• src/test-mass-diversity-generator.lua:31, 87, 123, 204 — four

test output directories.

• src/test-report-generator.lua:342 — test fixture path.
• libs/hope-card-formatter-test.lua:167 — test fixture path.
• libs/html-threaded/test.lua:12, 33, 60, 69 — test fixture path.

1. Delete scripts/parallel-word-pages.lua. The file was untracked,

never functional (ends in three IMPLEMENTATION INCOMPLETE error
lines), and is superseded by the design proposed in issue 10-035.

1. Skip libs/fuzzy-computing.lua. The file has no callers in tracked

code and its M.generate function is marked DEPRECATED. Migrating
its paths would imply ongoing maintenance the file does not warrant.
Flag for deletion in a follow-up.

Files involved

First pass

• scripts/ensure-tmp-symlink (new)
• scripts/update
• .gitignore

Second pass

• scripts/update-words
• scripts/start-ollama-cuda.sh
• src/centroid-generator.lua
• src/similarity-engine.lua
• src/generate-word-pages.lua
• src/ollama-manager.lua
• src/test-mass-diversity-generator.lua
• src/test-report-generator.lua
• libs/hope-card-formatter-test.lua
• libs/html-threaded/test.lua
• scripts/parallel-word-pages.lua (deleted)

Considerations

• The system tmpfs is 16 GB on the current development host. Peak ZIP

extraction working size has been observed at around 2.3 GB. If the
project is later deployed somewhere with a smaller tmpfs (a low-memory
VM, a Termux Android host), the extraction working directory may need
to revert to disk-backed storage. In that case, split the helper into
two: one for small ephemera (tmpfs) and one for large working sets
(disk-backed under a separate name).

• The helper enforces the symlink invariant by failing loudly rather

than auto-migrating an existing real directory. This follows the
project-wide principle "prefer error messages and breaking
functionality over fallbacks": a silent migration of someone's data
into tmpfs (where it evaporates on reboot) would be worse than a loud
refusal that prompts human attention.

• The portability gain from routing everything through the project-relative

tmp/ is concrete: two parallel checkouts of the same repository at
different paths produce ephemera at distinct tmpfs targets, with no
cross-talk. The previous raw /tmp/foo.json pattern was a hidden
source of cross-checkout collision.

• libs/fuzzy-computing.lua should be reviewed for deletion. Its M.generate

is marked DEPRECATED and a tree-wide search finds no require calls for
the module.

• The Lua audit suggested by issue 10-035 (parallelizing word page

generation) is still open. The work here makes that future change easier
by giving the to-be-spawned workers a stable, portable working directory.