Saar Ha-Panim is Metatron, my source is Rabbi Yoel D. Bakst from Colorado. The Gaon of Vilna mentions Metatron in Kol Hator.
I think the phrase translated as "minister of the interior" is from the Hebrew phrase "Saar Ha-Panim". Kol Hator states that Metatron is Yosef.
Here's a quote from Rabbi Bakst, who quotes Rav Hillel of Shklov in Kol Hator
The Twin Messiahs are the two pulsating currents of divine energy — din (or gevurah)/constriction and hesed/expansion — manifesting within the historical space-time of each and every generation. Although each messianic current is a distinct force field of energy that appears to repulse the other, it is the very tension they generate that, when channeled and directed, becomes the most powerful force for personal, national, and planetary change that has ever existed. Their paradoxical natures are continually present in every thought and action, and they are waiting to be channeled.
R. Hillel explains
A fundamental rule is that during the performance of every mitzvah and every tefilah, one should contemplate the unification [of the Trein M’shechin] and bind oneself to the "Two Armies of God" — [these being the two divine names] E-lohim Tzevaot (God of Armies) and Y-HVH Tzevaot (Lord of Armies), din (constriction) and hesed (expansion). One must [then] calculate the line of balance between their two numerical values — 499½ from the left side and 499½ from the right side.*
Each of the two messianic polarities has within itself a number of sub-currents that interact together in a cacophony of pulsating social, political, and religious events
to generate the ever-rising threshold of Formula 999. In a divinely orchestrated fashion they all act according to specific laws contained within the 156 Aspects of Mashiach ben Yoseph. It is they who make up the members of the Two Armies of God. In Kol HaTor's Messianic Conspiracy, they are the Appointed Agents of God.
R. Hillel writes
The thrice-woven cord of "Signs," "Designated Times," and "Appointed Agents" appears simultaneously in a three-pronged campaign. The "agents" react to the "signs" and thus accelerate the arrival of the "designated times." This is alluded to in the verse, "The blossoms have appeared in the land; the time of singing has arrived, and kol hator — the call of the turtledove — is heard in the land" (Song of Songs 2:12). "The blossoms have appeared" — these are the signs; "the time of singing has arrived" — these are the designated times; "the call of the turtledove is heard" — these are the appointed agents.*
These agents are vehicles for the different aspects, or mini-personalities which, like pieces in a puzzle, only when they are fit together constitute the totality of Mashiach ben Yoseph.43 They include, for example, names like Ephraim ben Yoseph, Shirya ben Dan,44 Eliyahu HaNavi (Elijah the Prophet), the archangels Gabriel, Sandalfon, and Metatron, Neriya, Menachem, Ezra and Nehemiah, Yehoshua ben Nun, Sasson and Simcha. (Sasson and Simcha are explained in Chapter 4, Metatron.)
There is, however, one all encompassing Mashiach ben Yoseph archetype that we must mention briefly. Initially it appears to confuse an already overly complex pantheon of messianic archetypes, yet it is precisely here where all the various aspects of Mashiach ben Yoseph come together. This is the climatic evolution of Formula 999 into the Great Thousand. This is the cosmic image of Moses our Teacher together with the Two Messiahs.
So I guess I'm saying that Metatron and Yehoshua Ben Nun are both agents of the Messianic Redemption, and that some of those agents have aspects of the others in them. Hanoch became Metatron, if I'm not mistaken. Maybe Yehoshua Saar Ha-Panim refers to the Metatronic aspect of Yehoshua Ben Nun.