feat: add trim and fallback_on_empty options to PostProcessConfig

[KaiStarkk]

Summary

Adds two new boolean fields to PostProcessConfig that give post-process scripts finer control over output handling:

• trim (default: true) — When set to false, only trailing newlines (shell artifacts) are stripped from command output, preserving all other whitespace. This is needed when a post-process script intentionally adds trailing spaces, e.g. appending a space after sentence-ending punctuation for smoother dictation flow.

• fallback_on_empty (default: true) — When set to false, empty command output is returned as an empty string instead of falling back to the original transcription text. This is needed when a post-process script intentionally outputs nothing to suppress unwanted transcriptions, e.g. filtering out [BLANK_AUDIO] markers.

Why this is needed

The current post-processing pipeline unconditionally calls .trim() on command output, which strips trailing spaces that some scripts add intentionally. It also unconditionally falls back to the original text when output is empty, which defeats scripts designed to suppress certain transcriptions.

These two behaviors are reasonable defaults, but they need to be configurable for legitimate use cases.

Backward compatibility

Both fields default to true, which preserves the existing behavior exactly. No configuration changes are required for existing users.

Config example

[output.post_process]
command = "my-dictation-formatter"
trim = false              # preserve trailing spaces from formatter
fallback_on_empty = false # allow formatter to suppress output

Tests

4 new tests added covering the new fields. All 16 post_process tests pass.

Files changed

• src/config.rs — Add trim and fallback_on_empty fields to PostProcessConfig with serde defaults and documentation comments; add config file comments
• src/daemon.rs — Populate new fields when constructing PostProcessConfig from profile overrides
• src/output/post_process.rs — Implement conditional trim and fallback logic in PostProcessor; add 4 tests