Honor the configured generator input file

[FrogAi]

Summary

• Open the PBF path provided through OfflineSettings.InputFile.
• Make mapd generate --input-file PATH select PATH instead of the hard-coded default.
• Preserve the existing ./map.osm.pbf CLI default.

Motivation

The generate command declares --input-file, defaults it to ./map.osm.pbf, and copies the parsed value into OfflineSettings.InputFile. GenerateOffline ignores that field and always opens the literal ./map.osm.pbf.

As a result, an explicit absolute or relative input works only when the default file also exists, and generation reads the default rather than the selected file. Conversely, a missing selected path is silently ignored when the default exists.

Implementation

GenerateOffline now passes s.InputFile to os.Open. The selected file then follows the existing scanner, generation, and error paths unchanged.

The CLI remains the owner of the default value, so omitting --input-file still supplies ./map.osm.pbf.

Behavior

Case	Base 68813e05	This change
Absolute selected file exists; default absent	Panics opening default	Generates from selected file
Relative selected file exists; default absent	Panics opening default	Generates from selected file
Selected file missing; default exists	Generates from default	Existing open-error panic
Selected path empty; default exists	Generates from default	Existing open-error panic
--input-file omitted; default exists	Generates from default	Unchanged

Validation

An external Linux oracle exercised the exported generator and a built CLI child process with a real locations-on-ways PBF fixture. Every successful case decoded the generated packed Cap'n Proto output and required one loaded tile containing ways.

• Base 68813e05 ignored absolute, relative, missing, and empty selections; the explicit CLI selection failed when no default file existed.
• The candidate used absolute and relative paths, rejected missing and empty selected paths through the existing open-error policy, and preserved direct and CLI default behavior.
• The complete focused matrix passed three repetitions under the race detector.
• go test ./..., go test -race ./..., go vet ./..., and go build ./... passed on Linux/amd64 with Go 1.25.1.
• FrogAi Actions Build #49 passed the exact commit 135f703f449f9227477aca978258abf7ae0afa56; the branch-push workflow ran its Build binary step.

Compatibility

• The CLI flag, alias, default, help text, settings field, output layout, scripts, and generated tile format are unchanged.
• Relative paths remain relative to the current working directory; absolute paths remain supported by os.Open.
• Missing and empty paths retain the existing log-and-panic error policy. Direct Go callers that leave OfflineSettings.InputFile empty must now provide the same explicit default that the CLI already supplies.
• PBF scanner-error handling remains the separate scope of PR Stop map publication on PBF scan errors #111.
• No dependencies, exported APIs, schemas, configuration keys, or file formats change.

Audit follow-up (head 92bfb64)

An independent audit confirmed the flag was genuinely dead — base hardcoded ./map.osm.pbf and silently ignored --input-file/-i — and that the default path is byte-identical to base behavior.

It also found that this change leaves the generate subcommand's own usage line stale, since it still advertised generation "from 'map.osm.pbf'" while the source is now configurable. Head 92bfb64 updates that text to refer to --input-file. FrogAi Build #54 passed for the exact head.

Pre-existing and not addressed here: an input path that opens but cannot be parsed — a directory, or a truncated pbf — still produces zero-way tiles over the requested bounds instead of failing loudly. That behavior is unchanged by this PR, but it becomes easier to reach now that the path is user-supplied.

Composition with #97 is clean, verified by trial merge, build, and test, with the way-assignment loop byte-identical to main and untouched by both PRs.