feat: make MIMI_TIMEZONE configurable via mimi_secrets.h

[joaosouz4dev]

Summary

Today MIMI_TIMEZONE is hard-coded to US Pacific (PST8PDT,M3.2.0,M11.1.0) in mimi_config.h. Every local timestamp emitted by the firmware — session log filenames, agent context, tool output, the existing get_current_time tool, localtime_r() calls throughout — is therefore wrong by anywhere between 4 and 16 hours for users outside the US west coast. Fixing it requires editing a git-tracked file, which is easy to forget when pulling upstream and noisy in PR diffs.

This patch promotes the value to the existing build-time secrets layer:

// mimi_config.h — secret fallback + alias
#ifndef MIMI_SECRET_TIMEZONE
#define MIMI_SECRET_TIMEZONE  "PST8PDT,M3.2.0,M11.1.0"
#endif
#define MIMI_TIMEZONE         MIMI_SECRET_TIMEZONE

Set MIMI_SECRET_TIMEZONE in mimi_secrets.h (gitignored, per-device) and you're done. Leave it unset and the default keeps the prior US Pacific value, so no existing build behaves differently.

What's in the diff

• main/mimi_config.h — MIMI_SECRET_TIMEZONE with #ifndef fallback (same pattern as every other secret in the file) and MIMI_TIMEZONE aliased to it.
• main/mimi_secrets.h.example — documented MIMI_SECRET_TIMEZONE slot with worked POSIX TZ examples for Brasília, Lisbon, London, Berlin, Tokyo, New York, plus a link to tzset(3).
• README.md — one-paragraph pointer in the "Configure" section.

No code-path changes: every caller already includes mimi_config.h and reads MIMI_TIMEZONE, so the substitution is transparent.

Test plan

• Default build (no mimi_secrets.h override): idf.py fullclean && idf.py build succeeds, MIMI_TIMEZONE still expands to "PST8PDT,M3.2.0,M11.1.0".
• Override build: set MIMI_SECRET_TIMEZONE "<-03>3" in mimi_secrets.h, rebuild, flash, and confirm localtime_r() output (e.g. via get_current_time tool or any session log) matches local wall-clock time in São Paulo.
• No new warnings from the preprocessor on either path.

Summary by CodeRabbit

Release Notes

• New Features

  • Added per-device timezone customization. Devices can now be configured with custom POSIX TZ strings, enabling flexible timezone settings tailored to regional requirements instead of the default Pacific timezone.

• Documentation

  • Added detailed timezone configuration guidance including accepted TZ formats and reference documentation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 66005ae3-e0b6-4c9a-a0bd-5747cfac79da

📥 Commits

Reviewing files that changed from the base of the PR and between bb10ea0 and 7929b21.

📒 Files selected for processing (3)

• README.md
• main/mimi_config.h
• main/mimi_secrets.h.example

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📝 Walkthrough

Walkthrough

This PR adds a new timezone configuration mechanism that enables per-device customization via secrets. The changes introduce MIMI_SECRET_TIMEZONE as a build-time macro and refactor MIMI_TIMEZONE to use it, while documenting the feature in both the example secrets file and the README with POSIX TZ format guidance.

Changes

Timezone configuration override

Layer / File(s)	Summary
Timezone configuration override mechanism main/mimi_config.h	MIMI_SECRET_TIMEZONE is added with a default POSIX timezone string and MIMI_TIMEZONE is updated to use MIMI_SECRET_TIMEZONE instead of a hardcoded value, enabling customization per device via mimi_secrets.h.
Secrets example and user documentation main/mimi_secrets.h.example, README.md	The example secrets file documents MIMI_SECRET_TIMEZONE with POSIX TZ format examples and reference guidance, and the README is updated to explain the new timezone configuration option.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Poem

🐰 Timezones now bend to our will,
A secret to shift, device to device,
From PST to wherever you're still—
Configuration's the sweetest spice!
hop hop 🌍

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: making MIMI_TIMEZONE configurable via mimi_secrets.h, which is the core objective of the PR.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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