Turn a mail into task candidates, and into nothing else (#246)

The extraction half. internal/email.Extractor asks the resident Qwen3-1.7B,
under a GBNF grammar, what one message requires of him, and returns at most
three short candidates with an optional date.

Everything it can produce is a row in `tasks` with status "candidate",
written through the intake seam #130 built for exactly this (Source
"email:<mailbox>", Evidence = the subject line). No reminder, no fact, no
note, no calendar event. That bound is the design: a reminder FIRES, so a
1.7B misreading "встреча была в четверг" as a future appointment would wake
him up about it, whereas a wrong candidate is a line he dismisses in one
click. A due date the model read out of the mail is stored on the candidate,
where no scheduler reads it — the review page sorts by it. Relative wording
("до пятницы") is deliberately left in the text rather than resolved to a
date the model would get wrong.

The prompt is written against the two things a small model does here: it
summarises when asked to extract, and it invents an obligation out of a
polite closing line. Hence the demand for a verb phrase, and an explicit
empty array — most mail contains no task, and a model with no way to say
"nothing" says something.

Wiring: core owns extraction because llama-server lives in core's process,
so the reader hands messages over a new ipc.MethodIngestMail. It is a Server
hook (like StepUp/UnlockFn), not a CoreAPI method — not a store operation,
and no CoreAPI implementation should have to carry it. The hook stays nil
without an `email` config block or without a llama-server phraser, so the
method answers ErrUnknownMethod: off unless configured, twice over. There is
no keyword fallback on purpose — "the subject became a task" is a mailbox
rendered as a to-do list, not extraction.

Privacy: junk is refused before the model is called, mail text is never
search input, extraction errors carry byte counts rather than the reply, the
stored evidence is a truncated subject, and the log line names the mailbox
and the UID only.

internal/config/config.go

@@ -150,6 +150,12 @@ type Config struct {
 	// absent ⇒ no evaluation loop at all. See MemoryEvalConfig.
 	MemoryEval *MemoryEvalConfig `json:"memory_eval,omitempty"`
 
+	// Email — mail ingestion (Vikunja #246). nil / absent ⇒ core refuses
+	// ipc.MethodIngestMail outright, so a mail reader cannot make Maven read a
+	// mailbox by merely existing. See EmailConfig; the IMAP host and credential
+	// live in the reader (cmd/mavmaild), never here.
+	Email *EmailConfig `json:"email,omitempty"`
+
 	// Praxis — the ecosystem attention-state service. When configured, maven
 	// calls the Praxis HTTP tools API for attention listing and item lifecycle.
 	// Maven never touches Praxis's database directly (ecosystem invariant: no
@@ -418,6 +424,26 @@ type MemoryEvalConfig struct {
 	MinConfidence float64 `json:"min_confidence,omitempty"`
 }
 
+// EmailConfig — core's half of the email reader: how many task candidates one
+// message may produce, and how long the extraction call may take.
+//
+// There is deliberately nothing about a mailbox here. Core does not connect to
+// IMAP, does not know an account exists, and holds no mail credential — the
+// reader daemon does, the same split mavpoll uses for the zenmoney token. This
+// block only says "extraction is allowed, with these bounds".
+type EmailConfig struct {
+	// MaxTasks — candidates per message. 0 ⇒ email.MaxCandidates (3).
+	MaxTasks int `json:"max_tasks,omitempty"`
+
+	// Timeout — per-message extraction budget. 0 ⇒ DefaultEmailTimeout. This is
+	// a Thinking model reading a mail; nobody is waiting on the answer, but a
+	// hung llama-server must not pin the reader's connection forever.
+	Timeout Duration `json:"timeout,omitempty"`
+}
+
+// DefaultEmailTimeout — extraction budget per message.
+const DefaultEmailTimeout = 2 * time.Minute
+
 // PhraserConfig — the LLM-backed phraser seam. The daemon spawns llama-server
 // as a managed subprocess and sends chat-completion requests to phrase nudge
 // and reminder messages. nil ⇒ the template-based Stub is used instead.
@@ -607,6 +633,12 @@ func (c *Config) applyDefaults() {
 		c.MemoryEval.Interval = Duration(DefaultMemoryEvalInterval)
 	}
 
+	// Same rule again: absent stays nil (⇒ mail ingestion refused), present gets
+	// the timeout default so `{}` is a valid "on with the defaults".
+	if c.Email != nil && c.Email.Timeout <= 0 {
+		c.Email.Timeout = Duration(DefaultEmailTimeout)
+	}
+
 	if c.Voice != nil {
 		if c.Voice.RouterThreshold <= 0 {
 			c.Voice.RouterThreshold = DefaultRouterThreshold