Save-nudge never fires (or fires too eagerly) outside UTC+0, and never fires for a project's first observation

[Alexter2003]

📋 Pre-flight Checks

• I have searched existing issues and this is not a duplicate
• I understand this issue needs status:approved before a PR can be opened

📝 Bug Description

The save-nudge mechanism (the MEMORY REMINDER system message injected by the UserPromptSubmit hook to prompt the agent to call mem_save) never fires in practice for non-UTC hosts, and never fires at all for a project's very first observation — regardless of timezone. Across 4 real projects and 15 sessions on my machine, this produced 0 observations ever saved, despite substantial work happening in every session.

Two independent root causes, both in parse_epoch() / the nudge-gating logic, shared verbatim between plugin/claude-code/scripts/user-prompt-submit.sh and plugin/codex/scripts/user-prompt-submit.sh (the plugin/opencode/engram.ts implementation only has the second bug — its toEpochSecs already normalizes to UTC correctly):

1. parse_epoch() parses naive sqlite timestamps as local time instead of UTC.

sessions.started_at and observations.created_at are written by sqlite as datetime('now'), which returns YYYY-MM-DD HH:MM:SS in UTC with no timezone marker. The final fallback branch of parse_epoch() parses this string without -u:

date -j -f "%Y-%m-%dT%H:%M:%S" "$TS" "+%s" 2>/dev/null \
  || date -j -f "%Y-%m-%d %H:%M:%S" "$TS" "+%s" 2>/dev/null \
  || date -d "$TS" "+%s" 2>/dev/null

date interprets the naive string in the host's local timezone, so the computed epoch is skewed by the host's UTC offset:

• Negative offsets (e.g. UTC-6, Latin America): the parsed epoch is pushed into the future relative to the real UTC epoch, so SESSION_AGE_SECS / ELAPSED come out negative or near-zero. The session/last-save always looks "just started," and the nudge condition (elapsed > 900) can never become true. The nudge never fires, for any project, ever.
• Positive offsets (e.g. UTC+1/+2, Spain/Europe): the parsed epoch is pushed into the past, so elapsed time is inflated. The nudge fires far too eagerly — potentially right after the 5-minute session-age floor, and repeating every cooldown window even right after a save.
• UTC+0 hosts happen not to notice, since local time equals UTC.

I confirmed both directions empirically:

Timestamp stored in sqlite (UTC): 2026-07-26 06:00:00

Real epoch (parsed with -u):                     1785045600
Buggy epoch, host TZ=UTC-6 (my machine):          <parses into the future — negative/near-zero elapsed>
Buggy epoch, host TZ=Europe/Madrid (UTC+1/+2):    1785038400   (2h in the past vs. real epoch)
Fixed epoch (forced -u), any TZ:                  1785045600   (correct in both cases)

2. All three hook implementations treat "no observations yet" as "session just started," so a project's first save can never be nudged.

if [ -z "$LAST_SAVE_AT" ]; then
  # No observations yet — no nudge (session might just be starting)
  echo "$OUTPUT"
  exit 0
fi

and the opencode equivalent:

// No observations yet — nothing to nudge about
if (lastObsEpoch === 0) return

If a project has never had an observation saved, this branch always short-circuits before the elapsed-time check, regardless of how long the session has been running. Since the nudge is the only automated mechanism nudging the agent to call mem_save in the first place, a project can never accumulate its first observation through this path — it's a cycle with no way out. Independent of bug #1, this alone guarantees 0 observations for any brand-new project.

🔄 Steps to Reproduce

1. Start a fresh project with the Claude Code (or codex) plugin enabled, on a host whose local timezone is not UTC+0 (e.g. TZ=America/Mexico_City or TZ=Europe/Madrid).
2. Start a session, send a first prompt (loads tools), then keep the session open and active past 5 minutes without ever calling mem_save.
3. Send further prompts past the 15-minute staleness threshold.
4. Observe the UserPromptSubmit hook output for each prompt (or check engram stats / engram projects list after a while).

✅ Expected Behavior

Once a session is older than 5 minutes and the last save (or project creation, if there's never been one) is older than 15 minutes, the hook should inject the MEMORY REMINDER system message — regardless of the host's timezone and regardless of whether the project has ever had an observation before.

❌ Actual Behavior

• On a UTC-6 host: the nudge never fires. Verified via engram stats — 15 sessions, 43 prompts, 0 observations, across 4 different projects, over multiple days of real work.
• On a simulated UTC+1/+2 host: the nudge fires far too early/too often (elapsed time inflated by the offset).
• On any host, for any project that has never had a single observation: the nudge never fires no matter how long the session runs, because of bug fix(store): handle NULL project values in user_prompts #2 independently of Error en export/sync: Scan error al convertir NULL a string en columna "project" de user_prompts #1.

🖥️ Environment

• Operating System: macOS
• Engram Version: 0.1.1 (plugin cache) / 1.20.0 (Homebrew CLI)
• Agent / Client: Claude Code (also reproduced the same root cause in the codex hook script; opencode shares bug fix(store): handle NULL project values in user_prompts #2 only)

📋 Relevant Logs

$ engram stats
Engram Memory Stats
  Sessions:     15
  Observations: 0
  Prompts:      43
  Projects:     none yet
  Database:     /Users/alexvas/.engram/engram.db

$ engram projects list
Projects (4):
  dotfiles       0 obs   1 session    1 prompt
  acatesystem    0 obs   8 sessions  29 prompts
  alexvas        0 obs   2 sessions   6 prompts
  docuai         0 obs   4 sessions   7 prompts

💡 Additional Context

I have a fix ready and verified for both root causes, in both the claude-code and codex bash hooks (forcing -u on every naive-timestamp date parse, and treating "never saved" as maximally-stale instead of "just started"), plus the equivalent fix for the opencode TypeScript implementation's bug #2. Happy to open the PR once this issue is approved, per CONTRIBUTING.md.